Any out there with some answers and explanations......

[LMav]

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Hey everybody....

I came across a few questions in topscore and am unsure about the answer choices. If anybody could help me out, i really appreciate it.

Here are the questions:

1) Upon ovulation in female humans, the oocyte is released into the a) ovary b) oviduct c) body cavity d) follicle e)endometrium.

2) A woman carries a sex-linked lethan gene that causes spontaneous abortions. She has 6 children. How many of her children would you expect to be boys? a) None b) 1 c) 2 d) 3 e) 4

3) Which of the following parasitic diseases or parasites of humans is not aquired by eating the parasite in food or water?
a) Giardia b) Taenia c) Trichriosis d) Ascaris e) Schistosomiasis
( Has anybody who has taken the DAT faced questions like these?)

4) In triangle ABC(not right-angle), BC=6, AC=3 and SinB=1/4. Find SinA?

5) With one fair die, find the probability of throwing 2 fours in five attempts.
a) (10*125) / (36 * 216)
b) 125 / (36 * 216)
c) (36 * 216) / 125
d) (36 * 216) / (10 * 125)
e) 1/36

6) What is the net ionic equation for the reaction?
HCl(aq) + NaOH(aq) -----------> H20(l) + NaCl(aq)
a) H3O+(aq) + OH-(aq) ----------> 2H2O(l)
b) Na+(aq) + Cl-(aq) -----------> NaCl(aq)
c) H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) ----------> H20(l) + Na+(aq) + Cl-(aq)
d) a & c
e) b & c

Answer given: 1)c 2)c 3)b 5)a 6)a

My DAT is coming up on 27th ( next wednesday). I am so very tensed studying and reading everybody's thought after their DAT. Any last moment suggestions please that would help me improve my score....

Thanks a lot in advance.....
(Sorry if the date shows up as 12th Jan, it was my system)

 

[LMav]

Come on SDNers, somebody who can help me.... please...🙁

 

[ddsnp]

The oocyte is released into the body cavity then the fallopian tubes grab it.

 

[LMav]

The oocyte is released into the body cavity then the fallopian tubes grab it.

Thanks ddsnp. I thought they go the fallopian tube first. Thanks for correcting me.

 

[puncho]

If you go back to review the test, they give you the solution to each question.

 

[LMav]

If you go back to review the test, they give you the solution to each question.

I dont have the new version in which the solutions are explained. so I was a bit skeptic. Thanks a lot.

 

[joonkimdds]

4) In triangle ABC(not right-angle), BC=6, AC=3 and SinB=1/4. Find SinA?

6) What is the net ionic equation for the reaction?
HCl(aq) + NaOH(aq) -----------> H20(l) + NaCl(aq)
a) H3O+(aq) + OH-(aq) ----------> 2H2O(l)
b) Na+(aq) + Cl-(aq) -----------> NaCl(aq)
c) H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) ----------> H20(l) + Na+(aq) + Cl-(aq)
d) a & c
e) b & c

Answer given: 1)c 2)c 3)b 5)a 6)a

About question # 4... it sounds like very simple trig question, but unfortunately I still couldn't find out the answer. When U had this question, was there a picture shown this it? because depends on the location of A and C, I say that the answer can be changed because when it says SinB, it's opposite over hypo so I think we need to know what the oppo is first then find what the hypo is. If there was no picture shown, I hope someone here know how to solve that question.

About question #6...when it says find the net ionic equation, that means eliminate the spectator ions and show the actual chemical change taking place. Take a look at (C). H and OH are combined so there is H2O on product side right? that's good, but Na and Cl are not combined and showed seperately on product side. that's not good. They are not combined at all so they are called spectator ions. So choice C can't be the answer. D and E says C is the answer so they are not the answer. r u with me so far?

If i remember it correct, spectator ions also means that they are combined and the precipitate shows up. Precipitation means solid, I think, and B shows that aq + aq -> aq, so this means there was no precipitation so B can't be the answer.

A shows that aq + aq => l....i for got what l stands for...but I believe as long as it's not aq, it's precipitation...-_-; I don't know if i m right.

 

[Flipper405]

for #6... none of them look right but a is the closest. I would think it would have to be H+(aq) + OH-(aq) -> H2O(l)

The total ionic would be
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) --> H2O(l) + Na+(aq) + Cl-(aq)

This shows that Na+ and Cl- are spectator ions. Remove those and you get the net ionic equation
H+(aq) + OH-(aq) --> H2O(l)

(l) = liquid, so there was a precipitation. (I think)

 

[joonkimdds]

for #6... none of them look right but a is the closest. I would think it would have to be H+(aq) + OH-(aq) -> H2O(l)

The total ionic would be
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) --> H2O(l) + Na+(aq) + Cl-(aq)

This shows that Na+ and Cl- are spectator ions. Remove those and you get the net ionic equation
H+(aq) + OH-(aq) --> H2O(l)

(l) = liquid, so there was a precipitation. (I think)

Flipper405~ I agree with you. I don't know where the hack H30 came up instead of H + OH => H2O.

Anyway, i got a question for you. I know that I used to know this when I took gen chemistry but it's been such a long time so i forgot it. precipitation means solid right?? (aq) is aqua means liquid, isn't it? so then what's the difference between (aq) and (l) ? both of them are liquid aren't they? so then both of them shouldn't be precipitation.

 

[Richnator]

aq means aqueous, meaning a solute is dissolved in a solvent. Liquid is just a phase, like ice is solid and water is liquid. Two totally different things, aq and l.

 

[Flipper405]

(aq) = aqueous, meaning dissolved in water
(s) = solid
(l) = liquid
(g) = gas

that's right actually... precipitation is only for solids. I think this is actually an acid-base reaction now that I think about it.

I found a website that has this exact reaction and has the net ionic I listed-
http://virtual.yosemite.cc.ca.us/lmaki/Chem142/chap_outlines/chapter12.htm

III. Neutralization and Salts

* Neutralization - one type of double replacement reaction
* Acid + Base ® Salt + water
* Net ionic equation shows what drives the neutralization reaction

example:

Molecular: HCl(aq) + NaOH(aq) --> NaCl(aq) + H2O(l)

Total Ionic: H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) -->Na+(aq) + Cl-(aq) + H2O(l)

Net Ionic: H+(aq) + OH-(aq) --> H2O(l)
--------------------------------------------------------------------------

Regarding question 4, you have to use the sine law:
a/sinA=b/sinB=c/sinC

you know that a (BC) = 6, b (AC) = 3, and sin B =1/4. Plug and chug.

6/sin A = 3/(1/4)

sin A = 1/2

 

[joonkimdds]

Do we need to know whether they r soluble or insoluble?

 

[LMav]

Thanks you guys... That helped me a lot. Do you guys have any last moment tips for me please...I am so very tensed with only 5 days to go...🙁

 

[isd121]

2) A woman carries a sex-linked lethan gene that causes spontaneous abortions. She has 6 children. How many of her children would you expect to be boys? a) None b) 1 c) 2 d) 3 e) 4

sex-linked disease can cause spontaneous abortions for a male child only.
probability of having a boy is 50%.
probability of having infected gene in boy is 50%.

so the probability of having a boy with infected gene (which cause spontaneous abortions) = .50 X .50 = .25 (which means 25%)

So there will be 25% boys with infected gene, 25% normal boys, 25% normal girls, and 25% girls carries infected gene.

In other words, 25% will die and 75% will be alive.
6 children are alive in this case.
6 children = .75

number of normal boys = (6/.75)*.25 = 2

so answer is (c) 2.

i am not good in explaning...hope it will make sense to you 🙂

Iqbal

 

[Flipper405]

sex-linked disease can cause spontaneous abortions for a male child only.
probability of having a boy is 50%.
probability of having infected gene in boy is 50%.

so the probability of having a boy with infected gene (which cause spontaneous abortions) = .50 X .50 = .25 (which means 25%)

So there will be 25% boys with infected gene, 25% normal boys, 25% normal girls, and 25% girls carries infected gene.

In other words, 25% will die and 75% will be alive.
6 children are alive in this case.
6 children = .75

number of normal boys = (6/.75)*.25 = 2

so answer is (c) 2.

i am not good in explaning...hope it will make sense to you 🙂

Iqbal

I understand everything but the first thing you said. Why does it have to be only in male children?

 

[ysk]

anyone know how you'd do #5? Questions like this give me a little trouble... i thought the answer would be B: 1/6 x 1/6 x 5/6 x 5/6 x 5/6.

 

[Flipper405]

anyone know how you'd do #5? Questions like this give me a little trouble... i thought the answer would be B: 1/6 x 1/6 x 5/6 x 5/6 x 5/6.

I'm also very interested in an explanation for #5... Getting a feel for these probability questionse seems to be very useful for the QR.

 

[LMav]

anyone know how you'd do #5? Questions like this give me a little trouble... i thought the answer would be B: 1/6 x 1/6 x 5/6 x 5/6 x 5/6.

I thought this would be C(5,2)/36*216..

Please correct me if I am wrong..................................
I can never seem to understand probability🙁.

 

[dat_student]

anyone know how you'd do #5? Questions like this give me a little trouble... i thought the answer would be B: 1/6 x 1/6 x 5/6 x 5/6 x 5/6.

it's definitely A

 

[LMav]

it's definitely A

Could you please explain it?

 

[joonkimdds]

I thought this would be C(5,2)/36*216..

Please correct me if I am wrong..................................
I can never seem to understand probability🙁.

I don't even understand what the question is asking...2 four in five? what's that?

 

[dat_student]

Could you please explain it?

I believe TopScore has a formula. I'll try to find the formula for u but it's definitely A. I'll post something by midnight.

it's a hypergeometric question.

Here are the hidden assumptions:

1) The experiment consists of a sequence of independent trials.
2) The probability of success is constant.

 

[Flipper405]

I don't even understand what the question is asking...2 four in five? what's that?

It's asking the probability of rolling a die (singular of dice) and getting the die to read "4" 2 times out of 5 rolls.

 

[joonkimdds]

It's asking the probability of rolling a die (singular of dice) and getting the die to read "4" 2 times out of 5 rolls.

when it said fair die, i thought it means they kill u fairly because u commited something really bad (sin).

 

[Flipper405]

when it said fair die, i thought it means they kill u fairly because u commited something really bad (sin).

They're saying fair to distinguish it from being "loaded", where the numbers don't show up evenly.

 

[isd121]

I understand everything but the first thing you said. Why does it have to be only in male children?

A female gets an X chromosome from each parent and to suffer from an X-linked recessive disease she has to get bad alleles from both parents. But, a male only gets an X chromosome from his mother—he’s a male because his dad gave him a Y chromosome.
males can not be carriers of X-linked recessive diseases; they either have the disease or they don’t. In contrast, females can be carriers which means that they are free of the X-linked disease they may pass on to their children.

🙂

 

[BenignDMD]

Could you please explain it?

n = number of chances
r = number you need to get correct
p = proablitly of success for one trila
q = prob. of failure on one trial

formaula is (nCr)*(p^r)*(q^(n-r))

nCr = 5*2 = 10

p^r = 1/6 ^2
q^(n-r) = (5/6)^3

therefor: (10*125)/(36*216)

 

[dat_student]

n = number of chances
r = number you need to get correct
p = proablitly of success for one trila
q = prob. of failure on one trial

formaula is (nCr)*(p^r)*(q^(n-r))

nCr = 5*2 = 10

p^r = 1/6 ^2
q^(n-r) = (5/6)^3

therefor: (10*125)/(36*216)

thanks, that's the hypergeometric formula. I couldn't explain it better.

 

[BenignDMD]

thanks, that's the hypergeometric formula. I couldn't explain it better.

I like answering ppl's questions, keeps the info fresh in my mind...I know you like to do the same dat_student 🙂

 

[Flipper405]

A female gets an X chromosome from each parent and to suffer from an X-linked recessive disease she has to get bad alleles from both parents. But, a male only gets an X chromosome from his mother—he’s a male because his dad gave him a Y chromosome.
males can not be carriers of X-linked recessive diseases; they either have the disease or they don’t. In contrast, females can be carriers which means that they are free of the X-linked disease they may pass on to their children.

🙂

How do you know it's X-linked as opposed to Y-linked?

 

[BenignDMD]

How do you know it's X-linked as opposed to Y-linked?

Males have X and Y, with the Y have fewer comparitive genes to than the X...Therefore, a mutation on the X chromosome will be expressed, because there is no homologous chromosome to "dominate it"...SO even if it is recessive, a male will never be a carrier, they will always have that trait or not...Women will express it only if they are homo for it...

 

[Flipper405]

Males have X and Y, with the Y have fewer comparitive genes to than the X...Therefore, a mutation on the X chromosome will be expressed, because there is no homologous chromosome to "dominate it"...SO even if it is recessive, a male will never be a carrier, they will always have that trait or not...Women will express it only if they are homo for it...

Yeah, I just went back and read the question again... it says its a woman carrying so that makes it clear it's X-linked as well 😳

Thanks for your help. 👍

 

[BenignDMD]

Yeah, I just went back and read the question again... it says its a woman carrying so that makes it clear it's X-linked as well 😳

Thanks for your help. 👍

no prob.

 

[isd121]

How do you know it's X-linked as opposed to Y-linked?

Sex-linked in females can only be X-linked because they don't have Y.

🙂

 

[isd121]

How do you know it's X-linked as opposed to Y-linked?

Sex-linked in females can only be X-linked because they don't have Y.

🙂

 

[Flipper405]

Sex-linked in females can only be X-linked because they don't have Y.

🙂

Yeah, I should have taken more time to read the question... 🙄

Thanks. 😀

 

[LMav]

n = number of chances
r = number you need to get correct
p = proablitly of success for one trila
q = prob. of failure on one trial

formaula is (nCr)*(p^r)*(q^(n-r))

nCr = 5*2 = 10

p^r = 1/6 ^2
q^(n-r) = (5/6)^3

therefor: (10*125)/(36*216)

I got it now. Thanks a lot Benign🙂. This probability always kills me. I dont know what I am gonna do on the test if I get such questions.....

 

[joonkimdds]

I think u guys know too much about sex....I barely passed sex education. -_-;