some bio, gchem and QR questions!!!

[bxs023100]

hey guys. i have a few questions from my achiever tests. if you could answer them, that would be awesome!!

BIO: ( test 1 )

4. static allele frequencies, leading to extinction of a species is related to what condition.

Q: how in the world is this question related to hardy-weinberg? the answer is genetic equilibrium.


GCHEM ( test 2)

20. what mass of chromium is theoretically obtainable from 1 kg ore containing 76% Cr2O3?

Q: in their solution, they have this: [(.76g Cr2O3)(1000)] / 152 g Cr2O3. from that equation they get 5 moles Cr2O3. Where is that 1000 from?

30. it is a question asking for average bond energy for N-F given all the other energies.
the equation is this: NH3 + 3F2 --> NF3 + 3HF ^H= -873.8

Q. The formula they use is ^H = -^H product + ^H reactant
in every book ive bought, the formula is: product - reactant. Did they use the wrong formula?

QR: (tests 1 and 2)

My main question from this section is that from the destroyer book, i was told that the permutation formula is this: nPr = n!/(n-r)! .and the combination formula is this: nCr = n!/r! x (n-r)! . i called someone at orgoman and they said the best way to distinguish whether the problem is combination or permutation is that permutation is slots, where combination is forming a group from given.

so in this problem: what is the probability of 3 heads and 2 tails from 5 consecutive tosses of a fair coin?
they used 5!/3!2!. they also stated in the solution that they were going to use the permutation formula.
isnt that the combination formula?

also, in these problems: how many different ways can a data set of 6,0,0,1,0,1 be arranged?
they also stated in the solution that they were going to use permutation, and the equation they set up was 6!/3!2!.

ok, well i have two more QR problems, but ill post them in another thread!! THANKS guys!!

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[Streetwolf]

My main question from this section is that from the destroyer book, i was told that the permutation formula is this: nPr = n!/(n-r)! .and the combination formula is this: nCr = n!/r! x (n-r)! . i called someone at orgoman and they said the best way to distinguish whether the problem is combination or permutation is that permutation is slots, where combination is forming a group from given.

so in this problem: what is the probability of 3 heads and 2 tails from 5 consecutive tosses of a fair coin?
they used 5!/3!2!. they also stated in the solution that they were going to use the permutation formula.
isnt that the combination formula?

It's a combination.

also, in these problems: how many different ways can a data set of 6,0,0,1,0,1 be arranged?
they also stated in the solution that they were going to use permutation, and the equation they set up was 6!/3!2!.

This one isn't really either one. There are six numbers so you have 6! on top. But you have three 0s and two 1s so that's where the 3! and 2! on the bottom come from. You also have one 6 so technically there could be a 1! on the bottom as well, but since 1! = 1 they don't include it.

ok, well i have two more QR problems, but ill post them in another thread!! THANKS guys!!

 

[bxs023100]

but in the first one, they said they were going to use the permutation formula. is that just a mistake on their part?

 

[Streetwolf]

but in the first one, they said they were going to use the permutation formula. is that just a mistake on their part?

Yes. Combination means order doesn't matter.

 

[Anemone]

hey guys. i have a few questions from my achiever tests. if you could answer them, that would be awesome!!

BIO: ( test 1 )

4. static allele frequencies, leading to extinction of a species is related to what condition.

Q: how in the world is this question related to hardy-weinberg? the answer is genetic equilibrium.


GCHEM ( test 2)

20. what mass of chromium is theoretically obtainable from 1 kg ore containing 76% Cr2O3?

Q: in their solution, they have this: [(.76g Cr2O3)(1000)] / 152 g Cr2O3. from that equation they get 5 moles Cr2O3. Where is that 1000 from?

30. it is a question asking for average bond energy for N-F given all the other energies.
the equation is this: NH3 + 3F2 --> NF3 + 3HF ^H= -873.8

Q. The formula they use is ^H = -^H product + ^H reactant
in every book ive bought, the formula is: product - reactant. Did they use the wrong formula?

QR: (tests 1 and 2)

My main question from this section is that from the destroyer book, i was told that the permutation formula is this: nPr = n!/(n-r)! .and the combination formula is this: nCr = n!/r! x (n-r)! . i called someone at orgoman and they said the best way to distinguish whether the problem is combination or permutation is that permutation is slots, where combination is forming a group from given.

so in this problem: what is the probability of 3 heads and 2 tails from 5 consecutive tosses of a fair coin?
they used 5!/3!2!. they also stated in the solution that they were going to use the permutation formula.
isnt that the combination formula?

also, in these problems: how many different ways can a data set of 6,0,0,1,0,1 be arranged?
they also stated in the solution that they were going to use permutation, and the equation they set up was 6!/3!2!.

ok, well i have two more QR problems, but ill post them in another thread!! THANKS guys!!

1KG=1000G

 

[legoland]

My main question from this section is that from the destroyer book, i was told that the permutation formula is this: nPr = n!/(n-r)! .and the combination formula is this: nCr = n!/r! x (n-r)! . i called someone at orgoman and they said the best way to distinguish whether the problem is combination or permutation is that permutation is slots, where combination is forming a group from given.

so in this problem: what is the probability of 3 heads and 2 tails from 5 consecutive tosses of a fair coin?
they used 5!/3!2!. they also stated in the solution that they were going to use the permutation formula.
isnt that the combination formula?

It's a combination.

also, in these problems: how many different ways can a data set of 6,0,0,1,0,1 be arranged?
they also stated in the solution that they were going to use permutation, and the equation they set up was 6!/3!2!.

This one isn't really either one. There are six numbers so you have 6! on top. But you have three 0s and two 1s so that's where the 3! and 2! on the bottom come from. You also have one 6 so technically there could be a 1! on the bottom as well, but since 1! = 1 they don't include it.

ok, well i have two more QR problems, but ill post them in another thread!! THANKS guys!!

They're both considered as permutation (with repeat items in there). Check out this link which explains:

http://www.mathwarehouse.com/probability/permutations-repeated-items.php

BTW, 5!/3!2! appears to look like a combination, but this is simply telling that you have 5!/3!2! = 10 ways of getting 3 heads & 2 tails in 5 tosses of a coin. Not a combination rule at all!

 

[PD3]

Q: in their solution, they have this: [(.76g Cr2O3)(1000)] / 152 g Cr2O3. from that equation they get 5 moles Cr2O3. Where is that 1000 from?

The questions said that they had 1 kg of ore, so would't there be 760 g of Cr2O3?

 

[tresbon]

The questions said that they had 1 kg of ore, so would't there be 760 g of Cr2O3?

Exactly, that's what the numerator tends to. OP has got it typed wrongly though.

It should be written as [(.76 )(1000)] g Cr2O3/ 152 g Cr2O3 per Achiever's soultion, instead of [(.76g Cr2O3)(1000)] / 152 g Cr2O3. That makes a key difference here.

 

[Streetwolf]

They're both considered as permutation (with repeat items in there). Check out this link which explains:

http://www.mathwarehouse.com/probability/permutations-repeated-items.php

BTW, 5!/3!2! appears to look like a combination, but this is simply telling that you have 5!/3!2! = 10 ways of getting 3 heads & 2 tails in 5 tosses of a coin. Not a combination rule at all!

Uhh the coin thing IS a combination. How many ways can you choose 3 flips out of 5 that are heads? It doesn't matter in what order you choose the 3 flips.

And the 5!/3!2! is NOT a combination but it's also not the same type of permutation that has been discussed here so many times. The formula is not n!/(n-r)!r!