dirty rats in my problem .pls solve it

[itsammy003]

1)40% of the rats included in an experiment were male rats ,if some of the rats died during the experiment and 30%of the rats that died were male rats ,what was the ratio that died were male rats,what was the ratio of the death rate among the male rats to the death rate among the female rats ?

answer is ) 9/14 how?

2)if half the people in a room leave at the end of every 5 minutes interval ,and at the end of twenty minutes the next to last person leaves ,how many people are in the room to start with

answer is 12 .how?

3) The length and breadth of a rectangular piece of land are in the ratio of 5:3 .the owner spent Rs 3000 for surrounding it from all the sides at the rate of $ 7.50 per meter ,the difference between length and breadth is
(i didnt understand why he gave here both $'s and Rs's .do we have to convert ?

answer is 50m

[itsammy003]

any answers?

[hahahut]

For question one: Let A be the overall population of rats and B be the overall population of dead rats. So the ratio for male rats is 0.3B/0.4A, and the ratio for female rats is 0.7B/0.6A. Now the ratio between male rats and female rats is (0.3B/0.4A)/(0.7B/0.6A), which is 9/14.

[hahahut]

Are you sure the answer to second question is 12? I feel it should be 16: X * 2^-4 = 1 => x = 16. If 12 is the right answer, at the end of 10th minute, there would be 3 in the room and half of them leaving...

For question 3, we know the perimeter of the land by 3000/7.5=>400. If the length of sides are 5X and 3X. Then we have (5x+3x)*2 = 400 => x=25. Therefore we get 50 for the difference.

[itsammy003]

yes thy correct answer is 16 . its mistake in the key

[colina]

2. (Question 2) We can beginning reversing the order:

2 at 20 min
4 at 15 min
8 at 10 min
16 at 5 min.

So 16 is te answer. As you mention before.

[Sadistic Sponge]

I'm sort of confused by the first one

EDIT: IGNORE THIS, it is incorrect!

I took a different approach to this and quickly made a percentage table:

_______I_Lived____I____Died__I__Totals
male___I_70%,28___I__30%, 12_I__100%, 40 (40% of population)
Female_I_30%,18___I__70%,42__I__100%, 60 (60% of population)
Totals__I_100%,46__I_100%, 54 _I__100____

I assumed a population size of 100 for this problem.

I was able to calculate every part of the table just fine, the part I'm struggling with now is:
",what was the ratio that died were male rats,"
Which immediately makes me ask if I am comparing 12:40 or 12:28?

what was the ratio of the death rate among the male rats to the death rate among the female rats"
The male rats had a death rate of 30%
The female rats had a death rate of 70%
Thats a 3/7 ratio...

This is frustrating me, as I have all the information I need but I know I'm doing something silly wrong...

[ramaricon]

Originally Posted by Sadistic Sponge

I'm sort of confused by the first one

I took a different approach to this and quickly made a percentage table:

_______I_Lived____I____Died__I__Totals
male___I_70%,28___I__30%, 12_I__100%, 40 (40% of population)
Female_I_30%,18___I__70%,42__I__100%, 60 (60% of population)
Totals__I_100%,46__I_100%, 54 _I__100____

I assumed a population size of 100 for this problem.

I was able to calculate every part of the table just fine, the part I'm struggling with now is:
",what was the ratio that died were male rats,"
Which immediately makes me ask if I am comparing 12:40 or 12:28?

what was the ratio of the death rate among the male rats to the death rate among the female rats"
The male rats had a death rate of 30%
The female rats had a death rate of 70%
Thats a 3/7 ratio...

This is frustrating me, as I have all the information I need but I know I'm doing something silly wrong...

what you are taking is that all the rats have died, that is the 30% of the rats that died were males doesn't signify that it's the 30% of the total male rat population but of the number of rats that have died. i hope it helps

[Sadistic Sponge]

So death rate= (deaths)/(Population of rats of x sex), right?

so death rate for males= 12/40=3/10
Death rate for females=42/60= 21/30=7/10

So the ratio between 3/10 : 7/10? I still don't think I understand...

[walt526]

hahahut's explanation is clear, why confuse the issue?

For question one: Let A be the overall population of rats and B be the overall population of dead rats. So the ratio for male rats is 0.3B/0.4A, and the ratio for female rats is 0.7B/0.6A. Now the ratio between male rats and female rats is (0.3B/0.4A)/(0.7B/0.6A), which is 9/14.