Current location - Training Enrollment Network - Mathematics courses - A bundle of exercise books is four yuan a box of pencils. Yuan Junjun wants to buy a bundle of exercise books and a box of pencils and give them to the salesman at the price of 100 yuan.
A bundle of exercise books is four yuan a box of pencils. Yuan Junjun wants to buy a bundle of exercise books and a box of pencils and give them to the salesman at the price of 100 yuan.
Suppose you buy x pens;
(a+2)x = 399 a+805；
x=(399a+805)/(a+2)
=[399(a+2)+7]/(a+2)
=399+7/(a+2)
7 is a prime number. If 7/(a+2) is a positive integer, only a+2=7, that is, a = 5；; x=399+ 1=400