Q30:
Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy?
(1) She bought $4.40 worth of stamps.
(2) She bought an equal number of $0.15 stamps and $0.29 stamps.
這題答案是A
由A中得出 0.15X+0.29Y=4.4然後可得X=10.Y=10時式子成立
我的疑問是有沒有更好的方法可以看出來這種式子的解有幾個呢?
我是用湊的..總覺得很不踏實的感覺!!!
請問有沒有比一個一個代入式子更有效率的方法??