Answer:
9 chairs
Explanation:
Let the complete question is,
"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 if during these two days, John and Larry assembled a total of 25 chairs."
Let last Thursday, John assembled chairs for x hours and last Friday, Larry assembled chairs for y hours,
So, total number of hours = x + y
∵ total hours of working = 7,
⇒ x + y = 7, .....(1)
Rate of assembling chairs for John = 3 chairs per hour,
Thus, the total chairs assembled by John = 3x,
Similarly, Rate of assembling chairs for Larry = 4 chairs per hour,
Thus, the total chairs assembled by Larry = 4y,
Total assembled chairs = 3x + 4y
∵ Total assembled chairs = 25,
⇒ 3x + 4y = 25 .....(2)
Equation (2) - 4 × equation (1),
3x - 4x = 25 - 28
-x = -3
⇒ x = 3
Hence,
The number of chairs assembled by John last Thursday = 3(3) = 9