GWD6-30

chriswendy36

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.

Answer: A

My Answer: C

Did I miss something here? The question looks too simple... Pls help!

chriswendy36

thanks a lot!

ecsniffers

The only thing you missed out is that the number of the $0.15 stamps and that of the $0.29 stamps must be integers

assurance

15x + 29y = 440

x >= 0, y >= 0且为整数，所以y必定能被5整除,
y = 5, 10, 15
很容易算出y=10,x=10是唯一解