Know the answer but need an explaination

Forum for the GRE subject test in mathematics.
GRE_Savvy
Posts: 1
Joined: Tue Jul 21, 2009 6:14 am

Know the answer but need an explaination

Postby GRE_Savvy » Tue Jul 21, 2009 6:32 am

Can somebody help me with this?

Question
If the ratio of the ages of two friends A and B is in the ratio 3 : 5 and that of B and C is 3 : 5 and the sum of their ages is 147, then how old is B?

1. 15 years
2. 75 years
3. 49 years
4. 45 years
5. 27 years


The answer is 45 years, but what is the correct approach to solve it?

User avatar
lime
Posts: 129
Joined: Tue Dec 04, 2007 2:11 am

Re: Know the answer but need an explaination

Postby lime » Tue Jul 21, 2009 10:51 am

A/B = 3/5
B/C = 3/5
A + B + C = 147.

Expressing from first two A = (3/5)*B and C = (5/3)*B, putting them into last one and multiplying all by 15 gives

9B + 15B + 25B = 147*15
49B = 2205
B = 45.

Btw., this forum is for mathematicians preparing for the GRE Subject Test, which is different from Quantitative Section of the GRE General test.




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