Last Thursday, John assembled chairs at a rate of 3 chairs

[BTGmoderatorDC]

Last Thursday, John assembled chairs at a rate of 3 chairs per hour for part of the day and Larry assembled no chairs. Last Friday, Larry assembled chairs at a rate of 4 chairs per hour for part of the day and John assembled no chairs. If John and Larry assembled chairs for a total of 7 hours during these two days, how many chairs did John assemble last Thursday?

(1) During these two days, John and Larry assembled a total of 25 chairs.
(2) During these two days, Larry assembled more chairs than John did.

OA A

Source: GMAT Prep

[Jay@ManhattanReview]

Last Thursday, John assembled chairs at a rate of 3 chairs per hour for part of the day and Larry assembled no chairs. Last Friday, Larry assembled chairs at a rate of 4 chairs per hour for part of the day and John assembled no chairs. If John and Larry assembled chairs for a total of 7 hours during these two days, how many chairs did John assemble last Thursday?

(1) During these two days, John and Larry assembled a total of 25 chairs.
(2) During these two days, Larry assembled more chairs than John did.

OA A

Source: GMAT Prep

Say John assembled chairs for j hours on Thursday; thus, Larry assembled chairs for (7 - j) hours on Friday.

The total number of chairs assembled by the two = 3j + 4(7 - j).

We have to get the value of 3j.

Let's take each statement one by one.

(1) During these two days, John and Larry assembled a total of 25 chairs.

=> 3j + 4(7 - j) = 25

Thus, j = 3 => 3j = 9. Sufficient.

(2) During these two days, Larry assembled more chairs than John did.

No unique answer of j. Insufficient.

The correct answer: A

Hope this helps!

-Jay
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