Question on ratios

stephkhaira wrote:The number of stamps Kyle had and the number of stamps Amy had were in a ratio of 5:3 respectively. After Kyle gave Amy 10 stamps, the ratio changed to 7:5. As a result of the gift, Kyle had how many more stams than Amy?

20
30
40
60
90


[spoiler]ans: 40[/spoiler]

The number of stamps that Kaye and Alberto had were in the ratio 5:3 respectively. After Kaye gave Alberto 10 of her stamps, the ratio of the number Kaye had to the number Alberto had was 7:5. As a result of this gift, Kaye had how many more stamps than Alberto?

20
30
40
60
900

GMATGuruNY wrote:

The number of stamps that Kaye and Alberto had were in the ratio 5:3 respectively. After Kaye gave Alberto 10 of her stamps, the ratio of the number Kaye had to the number Alberto had was 7:5. As a result of this gift, Kaye had how many more stamps than Alberto?

20
30
40
60
900

The answer choices imply that the values in the problem are all MULTIPLES OF 10.

Since K:A = 5:3, the following options are implied:
K=50, A=30
K=100, A=60
K=150, A=90
K=200, A=120.

After K gives away 10 stamps and A receives 10 stamps, the resulting values for K and A must be in a ratio of 7 to 5:
K=40, A=40
K=90, A=70
K=140, A=100.
We can stop here, since 140:100 = 14:10 = 7:5.

Thus, after the exchange, K-A = 140-100 = 40.

Mitch,
Your method is cool.

Regards,
Uva.
The correct answer is C.