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.
the answer is (D), but I think (1) is a little tough.
Does that mean we must try all mutiples of 0.29 (from 1 to 15), and then find out only 10 satisfy ?
You need to factor in a bit of observation. You only need to check 4 multiples of the second quantity of stamps, because no other multiple would allow you to have a total quantity ending in 0 cents.
0 (doesn't work, .15 doesn't divide 4.40)
5 (doesn't work)
15 (doesn't work)