The teacher wants to buy 70 pens, each 5 yuan. Deliver 10 when Store A is full, give 10% discount to Store B and return 1 0 when Store C is full. Which stationery store is more suitable for buying?

The teacher wants to buy 70 pens, each 5 yuan. When a store is full 10 to send 1, get

5×70=350 yuan

And because 10, you get one.

60 ÷ 10 = 6, [70-(60+6)] × 5+60× 5 = 320 yuan.

10% discount on the sales in store B, and 4.5×70=3 15 yuan is obtained.

Store C is full 100 yuan back 10 yuan, and it is obtained.

70×5=350 yuan, 300×10 = 30 yuan.

350-30 = 320 yuan

C > B < A

A: it's more cost-effective to buy it at store B.