b and c are postive numbes and 1/b=b/c=c/8 What is b+c? For

Question

b and c are postive numbes and 1/b=b/c=c/8

What is b+c?

For b, I am getting 1/8 and c=1

The choices are 

4
6
7
8
9

wonder_gmat · Answer

I get  6 .

...weird problem though!

ftoor · Answer

6 is the answer, how did you get it?

stolyar · Answer

{b^2=c
{c^2=8b

b and c are not zeroes

solve the system and get b=2 and c=4

2+4=6

wonder_gmat · Answer

To try a quick way, I looked at only the first two parts, disregarding c/8, because they give me some information about relation between  b  and  c .
1/b=b/c
 b┬▓ = c

Here since you know c = b┬▓, you could use this information in the equation b + c. 
b + c
= b + b┬▓
= b(b + 1)

This tells us that the answer should be the product of  b  and it's immediate follower: the only answer that satisfies this condition is  6 . 2(2 + 1) = 2*3 = 6.

Of course, the drawback of this technique is that you have to go with an intuition that  b  is an integer, otherwise you end up back and top and start all over again. But that doesn't take too long... probably like 30-40 seconds.

ann · Answer

from 1/b=b/c=c/8
b^2=c & b*c=8

So,
b* (b^2)=8
b=2

b*c=8
2*c=8
c=4

b and c are postive numbes and 1/b=b/c=c/8 What is b+c? For

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards