### Brain Teasers

# Stamps

"Dad wants one-cent, two-cent, three-cent, five-cent, and ten-cent stamps. He said to get four each of two sorts and three each of the others, but I've forgotten which. He gave me exactly enough to buy them; just these dimes." How many stamps of each type does Dad want? A dime is worth ten cents.

### Answer

The easy way to solve this is to sell her three each, for 3x(1+2+3+5+10) = 63 cents. Two more stamps must be bought, and they must make seven cents (since 17 is too much), so the fourth stamps are a two and a five.Hide Answer Show Answer

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## Comments

very good! i didn't think you could solve his one without knowing how many dimes you had but you proved me wrong

Excellent teaser. You explained it really good.

I used trial and error and got it pretty quickly, but I agree, your explanation/method is very well done.

nice teaser!!!

Nice solution, better than mine.

I figured one of the fours had to be an even-valued stamp and the other four had to be an odd value to have an even result. Since 1+2+3 = 6 can't be made a multiple of 5 by adding the even and odd from this group, the odd four had to be the five, which means the 2 has to be the other four. Less elegant, but it still only took a couple seconds to figure out.

I figured one of the fours had to be an even-valued stamp and the other four had to be an odd value to have an even result. Since 1+2+3 = 6 can't be made a multiple of 5 by adding the even and odd from this group, the odd four had to be the five, which means the 2 has to be the other four. Less elegant, but it still only took a couple seconds to figure out.

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