prep 41

41. 3308-!-item-!-187;#058&003278
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.
--------------------------------------------------------------------------------------------------------------------------------------------------------【答案】A
【思路】設John用x小時,Larry用y小時 x+y=7 問x=?
(1)3x+4y=25 ------------------------------------------------------------------- sufficient
(2)4y>3x ---------------------------------------------------------------------insufficient

这边的小，x, y 是整数么，为什么条件（2）insufficient 呢？