GWD 6, Q 30

dlmd

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.

any short cut to get answer is A, besides do all the calculation using trial and error?

[此贴子已经被作者于2005-2-7 2:23:05编辑过]

mikejia

15x+29y=440

要得出结果440各位数是0， 必须两个（15x和29y）个位都是0， 即：y是10的倍数；这里y只能是10，所以得出结果。

[此贴子已经被作者于2005-2-7 4:14:02编辑过]

dlmd

thanks