GMAT Prep2 (Voltage) ??

dferm · Posted: Wed May 14, 2008 5:18 pm Post subject: GMAT Prep2 (Voltage) ??

A certain meter records voltage between 0 volts and 10 volts, inclusive. If the average(arithmetic mean) value of 3 recordings on the meter was 8 volts, what was the smallest possible recording, in volts?

A. 2
B. 3
C. 4
D. 5
E. 6

Please Help..

Thanks..

Ans: A

AleksandrM · Posted: Wed May 14, 2008 6:18 pm Post subject:

I must be doing something wrong, but here is what I did:

I tried the first answer first:

2 + 2x/3 = 8 -----> x = 11 [impossible since it only records 0 to 10]

I would then say that 3 is the answer, but you say it is A.

I also tried plugging in the lowest reading of the answer choices (2) and the highest possible reading (10) and leaving the third reading as x:

2 + 10 + x = 24 ------> x = 12 [again, not possible given the limits].

I hope someone can throw some light on this one.

dferm · Posted: Wed May 14, 2008 6:22 pm Post subject:

The answer is C but I don't see how...

AleksandrM · Posted: Wed May 14, 2008 6:33 pm Post subject:

Ha ha. That is correct. Here is how. My 3 is wrong because you are supposed to assume that readings have to be in integers form, i.e., you cannot have 9.5

Here goes:

4 + 2x/3 = 8 [multiply both sides by 3 and subtract 4]

2x = 20 = 10

Since 10 is the highest reading that you can have, 4 is the answer.

2 is not the answer because you end up having a reading of 11, which is higher than the maximum, which is 10. And 3 is wrong because it gives you 9.5 which is not an integer.

The part about you having to assume that readings must be in integer form definitely throws one off.

Hope this helps.

AleksandrM · Posted: Wed May 14, 2008 8:11 pm Post subject:

My apologies about answer choice B. I was looking at the wrong side of my notes. The reason why B is not the answer is as follows:

3 + 2x/3 = 8

3 + 2x = 24

2x = 21

x = 10.5, which is more than the maximum reading, and is therefore the wrong answer.

Forget the whole integers/not integers fiasco from above.

Again, my apologies.

dferm · Posted: Wed May 14, 2008 8:12 pm Post subject:

Still don't understand this question...

Can you throw a little light on this question..

thanks.

dferm · Posted: Wed May 14, 2008 8:13 pm Post subject:

I don't understand how you are arriving with the equation 2x+3....

HELP....

AleksandrM · Posted: Wed May 14, 2008 9:04 pm Post subject:

The problem tells you that THREE readings were taken. It also asks you what was the LOWEST possible reading of the three readings taken. It also tells you that the AVERAGE of the three readings was 8. Now, you can pick one of the readings from your answer choices, as I have already showed you. The other two readings are unknown. Therefore, you assign the variable "x" to represent these readings. Therefore:

4 + x + x/3 = 8

When you add the Xs, you end up with 2x. The rest is just arithmetic.

Sorry, I should have been clearer before.

dferm · Posted: Wed May 14, 2008 9:08 pm Post subject:

GOT IT...

Thanks a billion...

ur the best...

AleksandrM · Posted: Wed May 14, 2008 9:18 pm Post subject:

No problem. Glad I could be of help.