Word problems similar to ratio but needing more?

Question

This is the same type of word problem that I missed..

I have seen the answers for a couple of variations, but still do not see where the answer is clear:
A certain drug is made out of two compounds only: compound A and compound B. To make this drug, 5 parts of compound A are used for every 8 parts of compound B. If a chemist has 305 milliliters of compound A, how many milliliters of this drug can be made?

The answers I can find is a ratio, but the answer of the compound A is still unclear...

Answer 1

5 parts of A : 13 parts total compound
305 milliters of A : x milliliters total compound

So 5/13 = 305/x

x = 305 * 13 / 5
x = 793 ml

Alternatively, you can do:
5/8 = 305/B
B = 305 * 8 / 5
B = 488 ml

Then add A (305 ml) plus B (488 ml) to get the total = 793 ml.

Answer 2

A piece of pie is just one part of the whole pie, which is cut up into eight equal pieces. Let's say your sister takes one piece and you take two.

The whole pie consists of 8 pieces of which your sister took one and you took two; so that 8 = 1 sis + 2 you + 5 no one is true. What is the ratio of pie you took? As 8 = 1 + 2 + 5, we can rewrite this as 1 = (1 + 2 + 5)/8 = 1/8 + 2/8 + 5/8; so you took a ratio of 2/8 of the pie.

So the deal is...identify all the parts of the whole thing first. In your problem you have two parts: A and B. So the whole drug = 5 (A) + 8 (B) = 13 parts and, like the pie, we do this 1 = (5 + 8)/13 = 5/13 + 8/13; so we have 5/13 as the A ratio and 8/13 as the B ratio.

THESE RATIOS REMAIN FIXED for this problem. Why, because any other ratios would not be that drug; it would be something else.

The sum of all ratios always adds up to one. Why? Because, that's how ratios are found...divide the sum into the terms (parts) of the sum to get 1.000 on one side of the equation and the ratios on the other side.

So, if we have 305 ml of A for that drug, Q = (5/13 + 8/13) Q because (5/13 + 8/13) = 1 the whole drug and anything multiplied by 1 is still the same number. Q is the total amount of the drug you are looking for. So 5/13 X Q = the A ml = 305 ml; and Q = 305 X 13/5; further 8/13 X Q = B ml = 8/13 X (305 X 13/5) = (8/5) X 305; so you can find the B amount as well.

Answer 3

Set up a ratio to find how much of compound B you can use with the amount of compound A you have.

5/8 = 305/x
5x = 2440
x = 488 ml of compound B

I guess if you add the 305 and 488 you'll get your answer for the drug.

Answer 4

Yes, You have to solve the problem the way you solved the first problem 300 / 2 * 5 = 750 Therefore 750 gms of flour is needed to make a cake for 5 people