Topscore 2 questions

[x-linked]

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1. OC which one has negative change in entropy?
2NO(g) + O2(g) ---- NO2(g)
H20(g) ---- 2H2O(l) answer is 2nd one
😕

2. QR probability of obtaining consecutive heads or tails in four tosses of an ordinary coin? answer is 1/16
i think it should be 2/2^4=1/8


3. QR a manufacture can complete a 5000 piece order in 4 days, while a different manufacture complete same order in 5 days. how many days will it take to complete your order if you use both at the same time? answer is 3
is it 5000/(5000/4)+(5000/5)= 2.2 so i chose 2, why its 3?

 

[x-linked]

4. OC the hybridization of the carbon atom indicated here is ? answer is sp
it is -CH=C=CH- for the central C

5. OC ochem question no.81, i cannot write here coz it is all aromatic ring, some1 please check and help me!!!

6. OC ochem question no.89, i cannot write here coz it is ring conformation change,
some1 please check and help me!!!

 

[Rezdawg]

1. you are going from a gas state to a liquid state...Losing entropy.

2. 1/2 * 1/2 * 1/2 * 1/2 = 1/16

3. If they do it in 2.2 days, then they cannot do it within 2 days. Thus, it will take them 3 days to accomplish it.

 

[Rezdawg]

4. If C was attached to 4 items, it would be sp3. If attached to 3, it would be sp2. If attached to 2, like in this example, it is sp.

5 and 6. I dont have the topscore available right now.

 

[HBomb]

Just to clarify here too, the answer to the probability question (#2) is 1/8, that is P(HHHH) + P(TTTT) = 1/16 + 1/16 = 1/8. This was a TopScore mistake.

 

[x-linked]

1. you are going from a gas state to a liquid state...Losing entropy.

QUOTE]

but for the first one, 2NO +O2---2NO2 before reaction 3mol gas after reaction 2mol, there should be entropy decrease

topscore has so many mistakes

 

[joy2dmd]

Just to clarify here too, the answer to the probability question (#2) is 1/8, that is P(HHHH) + P(TTTT) = 1/16 + 1/16 = 1/8. This was a TopScore mistake.

No topscore is right.
(1/2)*(1/2)*(1/2)*(1/2)=1/16
When two events are independent of each other, you must multiply to find the favorable outcome or probability.

 

[HBomb]

No topscore is right.
(1/2)*(1/2)*(1/2)*(1/2)=1/16
When two events are independent of each other, you must multiply to find the favorable outcome or probability.

No, really, you and TopScore are wrong, based on the question given by the OP:

2. QR probability of obtaining consecutive heads or tails in four tosses of an ordinary coin? answer is 1/16
i think it should be 2/2^4=1/8

 

[boogaking]

after looking this over I think Joy is right... I think TS is right... probability sux! What's the probability of getting a probability question on the DAT???

 

[x-linked]

topscore is wrong it is 2/16=1/8 i asked my professor already

 

[Rezdawg]

1/8 is correct...I didnt read the question right the first time.

Probability of obtaining 4 consecutive tails...1/16
Probability of obtaining 4 consecutive heads....1/16

Since it is saying "or", you add the two probabilities...1/8.

 

[joy2dmd]

1/8 is correct...I didnt read the question right the first time.

Probability of obtaining 4 consecutive tails...1/16
Probability of obtaining 4 consecutive heads....1/16

Since it is saying "or", you had the two probabilities...1/8.

What? You seem to be miss reading this question. Why are you combining tails and heads. The question states 4 heads or 4 tails consecutively, meaning in a row. For example, toss a coin, what's the prob that its heads, 1/2. Toss it again, it is an independent event from the first toss. What is the prob that the second toss is heads 1/2. 4 tosses IN A ROW are heads, 1/2 * 1/2 * 1/2 * 1/2. That's the end of the question. The "or" does not give additional possibilites. It is 4 heads or 4 tails in a row, that's it. You get four tosses.

Who is this "professor". Give me the name. I'll call him or her. I'm a stats TA and professor or not, my text book is pretty clear on this. It's a simple coin toss question of probability.

I'm sticking with topscore's answer because my text book verifies it.

 

[joy2dmd]

What? You seem to be miss reading this question. Why are you combining tails and heads. The question states 4 heads or 4 tails consecutively, meaning in a row. For example, toss a coin, what's the prob that its heads, 1/2. Toss it again, it is an independent event from the first toss. What is the prob that the second toss is heads 1/2. 4 tosses IN A ROW are heads, 1/2 * 1/2 * 1/2 * 1/2. That's the end of the question. The "or" does not give additional possibilites. It is 4 heads or 4 tails in a row, that's it. You get four tosses.

Who is this "professor". Give me the name. I'll call him or her. I'm a stats TA and professor or not, my text book is pretty clear on this. It's a simple coin toss question of probability.

I'm sticking with topscore's answer because my text book verifies it.

Here are some quick references on probability. Consider a single roll of a dice for questions also. What's the chance of rolling a 3 four times consecutively with a single die? 1/6*1/6*1/6*1/6

mulitiplication probability rule for independent events:

http://www.mathgoodies.com/lessons/vol6/independent_events.html
http://www.une.edu.au/WebStat/unit_materials/c5_inferential_statistics/probability.html

http://www.ma.umist.ac.uk/servicemaths/helm/ch4/4_3addmultlaws.pdf

🙂

 

[Rezdawg]

What? You seem to be miss reading this question. Why are you combining tails and heads. The question states 4 heads or 4 tails consecutively, meaning in a row. For example, toss a coin, what's the prob that its heads, 1/2. Toss it again, it is an independent event from the first toss. What is the prob that the second toss is heads 1/2. 4 tosses IN A ROW are heads, 1/2 * 1/2 * 1/2 * 1/2. That's the end of the question. The "or" does not give additional possibilites. It is 4 heads or 4 tails in a row, that's it. You get four tosses.

Who is this "professor". Give me the name. I'll call him or her. I'm a stats TA and professor or not, my text book is pretty clear on this. It's a simple coin toss question of probability.

I'm sticking with topscore's answer because my text book verifies it.

Right...you get only 4 tosses. Here are all the outcomes possible:

4 Heads : 1/16
3 Heads, 1 Tail : 3/16
2 Heads, 2 Tails : 8/16
1 Head, 3 Tails : 3/16
4 Tails : 1/16

Those are all the combinations you can have with 4 tosses.

Let me ask you this...What if it asked the probability of obtaining 2 heads/2 tails OR 1 head/3 tails??? How do you answer that? You ADD the probabilities...In this case, the answer would be 11/16 that you get either 2 heads/2 tails OR 1 head/3 tails.

The same method is applied to all heads or all tails....you add the probabilities.

 

[BiOGoly]

I agree with joy2dmd. It's easy to misinterpret a lot of these questions based on previous ones that are similar in format.

 

[HBomb]

I agree with joy2dmd. It's easy to misinterpret a lot of these questions based on previous ones that are similar in format.

...and that's exactly what you're doing.

 

[joy2dmd]

Right...you get only 4 tosses. Here are all the outcomes possible:

4 Heads : 1/16
3 Heads, 1 Tail : 3/16
2 Heads, 2 Tails : 8/16
1 Head, 3 Tails : 3/16
4 Tails : 1/16

Those are all the combinations you can have with 4 tosses.

Let me ask you this...What if it asked the probability of obtaining 2 heads/2 tails OR 1 head/3 tails??? How do you answer that? You ADD the probabilities...In this case, the answer would be 11/16 that you get either 2 heads/2 tails OR 1 head/3 tails.

The same method is applied to all heads or all tails....you add the probabilities.

Please read my http links if you still disagree. I really think you should, but if you don't, oh well.

You simply do not add probabilites in this example of a consecutive coin toss. You multiply. A coin only has two outcomes, its 50/50 each INDEPENDENT toss. If you combine tosses, wanting to get 4 heads in a row, you multiply.

Read the links. Read the links. Each toss is independent, period. If you have independent events, and you want the same outcome consecutively, you use the multiply rule. That is exactly what the rule says. It's not my rule, it's math which is an exact science, not business or dentistry that has several ways to do it. It's not asking combinations or permutations. Simple the probability of 4 heads in a row. Saying "or 4 tails in a row" is irrevelent information in this question because that is the only other outcome available. The probability of 4 heads in a row is the same as the probabiliyt of 4 tails in a row. The question is the same whether this is in there or not. If you want make it dependent events...e.g. 4 heads followed by 4 tails. Then the first condition is dependent upon the next and the probability changes and the answer will be a smaller number or lesser probability of the outcome.

I'm done trying to convince here. Just read the literature.
Cheers.

 

[HBomb]

Rezdawgs was just trying to save some key strokes, but I'll spell it out fully. It's just a binary problem. I'm listing out all the possibilities below. I'm not trying to argue that you multiply these independent tosses. I agree that the prob of getting HHHH is done by multiplying 0.5 and is (1/2)^4. I agree that the prob of getting TTTT is (1/2)^4. But what I don't agree on is the prob of getting 4 consecutive heads (HHHH) OR 4 consecutive tails (TTTT) in four tosses of a coin, as the question states. The prob of this is 1/16 + 1/16 = 1/8. Or you can just think of this as 2/16 = 1/8. Just look at the list I've constructed below. The question is confusing though. IF it asked: what is the prob of 4 heads in a row, or what is the prob of 4 tails in a row (compound sentence) then the answer is 1/16. OR if the question asked, what is the prob of 4 heads in a row, then 1/16. OR if the question asked, what is the prob of 4 tails in a row, then 1/16. But it doesn't ask that. It asks: probability of obtaining consecutive heads or tails in four tosses (in one question, non-compound sentence). That's why the answer is 2/16 or 1/8. Again, look at the 16 possibilities below:

1. HHHH <----------- four consecutive heads, one of the 2 possibilites we want
2. HHHT
3. HHTH
4. HHTT
5. HTHH
6. HTHT
7. HTTH
8. HTTT
9. THHH
10. THHT
11. THTH
12. THTT
13. TTHH
14. TTHT
15. TTTH
16. TTTT <-------- four consecutive tails, the other possibility we want

Also, I checked out the websites you posted, and the second website states this (from http://www.une.edu.au/WebStat/unit_...robability.html) "rule" which applies to our discussion:
"Another rule discussed in your texts is the addition rule. This simply states that for mutually exclusive events, the probability of either one or the other of the two events occurring is equal to the sum of the two probabilities."

PS. I love to argue, so granted, it is one of my faults. But please, as you state, be done with trying to convince anyone, because you're just convincing them of the wrong thing.

 

[Rezdawg]

Yes, I was trying to save time by not typing it out. 😀

But, HBomb came through despite my laziness...and he is correct.

 

[joy2dmd]

Yes, I was trying to save time by not typing it out. 😀

But, HBomb came through despite my laziness...and he is correct.

I stand corrected. Thanks.
🙂