If Jake loses 8 pounds, he will weigh twice as much as his sister. Together they now weigh 278 pounds. What is Jake's present weight, in pounds?

(A) 131
(B) 135
(C) 139
(D) 147
(E) 188

(x-8) = 2s

s+x = 278 --> s= 278-x

x-8 = 2(278-x)

3x=564

x=188

Hi All,

This question can be solved with fairly straight-forward Algebra (as the other solutions have proven). It can also be solved by TESTing THE ANSWERS and a bit of logic.

We're told that the total weight of Jake and his sister is 278 pounds. We're also told that if Jake lost 8 pounds, then he would weight TWICE as much as his sister. This means that, right now, Jake weighs MORE than TWICE his sister. We're asked for Jake's current weight.

Since Jake weighs more than twice his sister, his weight is MORE than 2/3 of the 278 pounds. Looking at these answer choices, I would TEST one of the bigger values first... Under normal circumstances, that would be Answer D. With a quick estimate though we can see that 2/3 of 270 pounds would be 180 pounds, but Jake has to weight MORE than that, so I'm going to TEST Answer E first....

If Jake weights 188 pounds...
Jake - 8 = 180 pounds....
Sister = 90 pounds
90 + 180 + 8 = 278 pounds
This is a MATCH for the information in the prompt, so Jake MUST weight 188 pounds.

Final Answer:

GMAT assassins aren't born, they're made,
Rich
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You can also test the answers.
When you realize that when you choose 188 for Jake's weight you get from the equations, a nice round number for his sister age and the work involved is fast:
J-8=2S, where J stands for Jake and S for his sister --> 188-8=2S --> S=90.
Now you can plug in the obtained value in the second equation: J+S= 278 --> As we have chosen 188 for Jake and got 90 pounds for his sister--> 188+90=278. This is a match. Option E is the correct answer.

One of my favorite method to attempt questions is by using as low level an approach as possible:

- On this question we know that 278 is the current sum of Jake's and his sister weights

- We also know that 270 is the sum of their weights if Jake loses 8 pounds

- Since 270 equals 2 parts from Jake's weight and 1 part from his sister weight so we can have following ratio

- Jake: 2 parts of 270 (180) and Sister: 1 part of 270 (90)

- So Jake's current weight will be those 2 parts (180) plus the weight that he has not lost yet (8) = 188 (option E)

- In fact we don't even need to calculate 188. Since we know that Jake's weight is at least 180 and since none of the other options is anywhere close to 180, so our answer is automatically option - E. Moreover, if you are pressed for time then you don't even have to consider 8. You can use the approximation technique to divide 278 into 3 equal parts which will be about ~93 and so Jake's weight is approximately 186 (and so only option E works)

\(? = 2M\)

\(\left\{ \matrix{
\,2M - 8 = 2S \hfill \cr
\,2M + S = 278 \hfill \cr} \right.\,\,\,\,\, \cong \,\,\,\,\left\{ \matrix{
\,M - S = 4 \hfill \cr
\,2M + S = 278 \hfill \cr} \right.\,\,\,\,\,\,\mathop \Rightarrow \limits^{\left( + \right)} \,\,\,\,\,\left( {{2 \over 3}} \right)3M = \left( {{2 \over 3}} \right)\left( {270 + 12} \right)\,\,\,\,\, \Rightarrow \,\,\,\,\,? = 2M = 2 \cdot 94 = 188\)


We follow the notations and rationale taught in the GMATH method.

Regards,
Fabio.
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Fabio Skilnik :: GMATH method creator (Math for the GMAT)
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