mixture problem

15x + 50(4-x) = 30*4
35x = 80
x=2.28
Answer C

Same as durgesh79
A+B=4----------(1)
0.15A+0.50B=(30/100)*4-------(2)

Solving for A we get A = 2.28..
Answer is C.

Learned this new easy method from Mukul's video.
Prepare table as follows :

A B
Ratio
Quantity
Strength 15 50
30
20 15

This gives new ratio of Mixture A and B as 20:15 i.e 4:3

Actual Ration for Mixture A is 4/7. Times 4 gallons is 2.28 Approx. equal to 2.3

So, you can set up the following equation:
let x = mixture A, y= mixture B

0.15x + 0.5 y = 4 * 0.3
x+ y = 4.

One thing I learn about preparing for GMAT PS question type is to understand the concept and basic. Then, after I am comfortable with the basic, I work on speed. I thought that there is no use learning for speed when my foundation is shaky.

I use this high school math web site to practice for word problem. It has good practice problems and if I can't get them or solve them comfortably within 2 minutes, what's my chance at beating the gmat?

https://www.oojih.com/show/wordproblem/mixture/

Using the alligation method (https://wps.prenhall.com/wps/media/objec ... c/ch07.pdf):

A=15%, B=50% => 4gals of 30%



A will be 20/35 = 4/7 of the mixture.

4/7 * 4 gals
= 16/7
= 2 and 2/7 (which is less than 2.5),
so the answer is answer choice C.

in a new solution we have the following proportion -
A/B=(50-30)/(30-15) =4/3
so now we know that A is 4/7 of the new solution of 4-gallon mixture or 4/7*4=16/7 or 2.3

hope it is a quick method and i could help u