What is the sum of a, b and c?

[vittalgmat]

What is the sum of a, b, and c?

1. ac = 3:4:7
2. c - a = 12

[spoiler]OA: C[/spoiler]

Pls explain

thanks

[Stuart@KaplanGMAT]

What is the sum of a, b, and c?

1. ac = 3:4:7
2. c - a = 12

Pls explain

thanks

Q: a+b+c = ?

(1) from a ratio, we can't determine any exact numbers: insufficient.
(2) no info about b: insufficient.

Together:

From (1), we know that a/c = 3/7. From (2), we know that c = a + 12. Combined, we know that a/a+12 = 3/7. We can solve this equation for a, then use the ratio to solve for both b and c: sufficient.

Together sufficient, apart insufficient: choose (C).

[maihuna]

There is a simpler way doing that:

1. ac = 3:4:7
2. c - a = 12

we know c = 7x a = 3x so c-a = 4x = 12 = > x = 3

so the numers are 3x 4x 7x i.e. 9 12 21 and so a powerful scientfic calculator can be used to determine a + b + c

and so CCCCCCCCCCCCC

[vittalgmat]

Silly me!!!. I was very close to the answer


Thanks Stuart and Maihuna for excellent explanation.