Data Sufficiency

Last Thursday, John assembled chairs at a rate of 3 chairs per hour for part o f 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.

piyush2694 wrote:Last Thursday, John assembled chairs at a rate of 3 chairs per hour for part o f 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.

Let J = the number of hours that John works.
Since John assembles 3 chairs per hour, the number of chairs assembled by John = 3J.
Let L = the number of hours that Larry works.
Since Larry assembles 4 chairs per hour, the number of chairs assembled by Larry = 4L.
Since John and Larry work a total of 7 hours, J+L = 7.

Statement 1:
3J + 4L = 25.
Since we have 2 variables (J and L) and two linear equations (J+L=7 and 3J+4L=25), we can solve for the 2 variables, allowing us to determine the number of chairs assembled by John.
SUFFICIENT.

Statement 2:
Case 1: J=3 and L=4, with the result that the number of chairs assembled by John = 3J = 3*3 = 9 and that the number of chairs assembled by Larry = 4J = 4*4 = 16
Case 2: J=2 and L=5, with the result that the number of chairs assembled by John = 3J = 3*2 = 6 and that the number of chairs assembled by Larry = 4J = 4*5 = 20
Since the number of chairs assembled by John can be different values, INSUFFICIENT.

The correct answer is A.