GMAT Prep Questions

[okigbo]

The number of stamps that Kaye and Alberto had were 5:3. After Kaye gave 10 of her stamps to Alberto, the ratio became 7:5. As a result of this gift, Kaye had how many more stamps than Alberto?
a. 20
b. 30
c. 40
d. 60
e. 90

Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate will be needed to complete the job in 8 days?
a. 2
b. 3
c. 4
d. 6
e. 8

Thanks

[aa2kash]

number one:
As the stamps are in the ratio 5:3
say kaye has 5x and alberto has 3x. then after kaye gave 10 stemps to alberto.
kaye= 5x-10
alberto=3x+10 and the new ratio is 7:5
solve this: 5x-10/3x+10=7/5 u will get x=30.

the difference in the stemps is 5(30)-3(30)=60

the Answer is D 60.

number two :

6*12 = 72 machine-days are required.
let x machines will finish the job in 8 ,then total 8x machine-days are required.
8x=72 -- x=9
therefore 3 additional machines are required.

Answer is B

[real2008]

ans are C,B respectively

[aa2kash]

ok. I misread the last line.we have to tell the number of stamps after kay gave 10 stemps to alberto.
as we have solved x=30.
Kay has 5x-10= 140 stamps
Alberto has 3x+10= 100 stamps

difference is 40 stamps.
Answer is c

[okigbo]

Thanks! I thought in the first problem that the equation was 5x-10/3x+10=7y/5y and couldn't solve the problem under 2 mins. Does anyone know why we add a variable to the second part of the ratio equation in some problems and not in others? I'm unclear on that.