Data Sufficiency

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.

The OA is A

Source: GMAT Prep

Let John's chair per working hour = j
Let Larry chair per working hour = l
$$j+l=7$$
Statement 1=> During these two days, John and Larry assembled a total of 25 chairs
$$3j+4l=25\ \ \ \ \left(from\ workdone=rate\cdot time\right)$$
$$j+l=7$$
$$l=7-j$$
Substitute the value of 'l' into the above expression,
$$3j+4\left(7-j\right)=25$$
$$3j+28-4j=25$$
$$-j=-3$$
$$j=3$$
So, John assemble 3*3=9 chairs. Hence, statement 1 is SUFFICIENT

Statement 2=> During these two days, Larry assembled more chairs than John did. This statement does not provide us with the total number of chairs they assembled. Therefore, statement 2 is NOT SUFFICIENT.

Since statement 1 alone is SUFFICIENT; then we have the correct answer to be option A.

Thanks