Is Barron's wrong?

Test Preparation SAT Preparation
1

<p>This is regarding Barron's 2400. Page 229 in Arithmetic. Question4.</p>

<p>Yan needs $2.37 in postage to mail a letter. If he has 60-cent, 37-cent, 23-cent, 5-cent, and 1-cent stamps (at least 10 of each), what is the smallest number of stamps he can use to get the exact postage he needs?</p>

<p>The answer, according to the book, is 8. Here's their explanation:

[quote]
Yan's goal is to use the fewest stamps, so start by seeing how many 60-cent stamps he can use without getting too high. Dividing 247 by 6 gives 3 with a remainder of 57. Using one 37 cent stamp leaves 20 cents, which Yan get with four 5-cent stamps, for a total of 8 stamps. No other combination uses fewer than 8 stamps.

[/quote]
</p>

<p>BUT, I found a combination that uses 7 stamps:</p>

<p>2 x 60-cent stamps = $1.20
3 x 37-cent stamps = $1.11
1 x 5-cent stamp = $0.05
1 x 1-cent stamp = $0.01</p>

<p>Adding all of them = $ 2.37</p>

<p>And that's just 7 stamps. Am I going wrong somewhere?</p>

2

<p>what are the answer choices?
And yes, they are wrong. The people who wrote these books are human too. lol</p>

3

<p>The choices are:</p>

<p>A) 6
B) 7
C) 8
D) 9
E) 13</p>

<p>Yes, but I'm worried. See, this was an easy question. What if a similar question comes in the SAT, but with larger numbers? I can't try all the thousands of combinations manually! Is there any mathematical way of doing this? :(</p>