SOLUTION: A stamp collection of 5,13, and 18 cent stamps. The number of 13 cent stamps is one less thatn twice the number of 5 cent stamps. The nubmer of 18 cent stamps is five more than t

Question 97036: A stamp collection of 5,13, and 18 cent stamps. The number of 13 cent stamps is one less thatn twice the number of 5 cent stamps. The nubmer of 18 cent stamps is five more than the number of 13 cent stamps. The total value of all the stamps is $2.60. Find the number of 13 cent stamps in the collection.
Answer by coyote(32) (Show Source): You can put this solution on YOUR website!
5 cent stamp = n
13 cent stamp = 2n-1
18 cent stamp = 2n-1+5
So
.05n + .13(2n-1) + .18(2n-1+5) = 2.60
.05n+ (.26n-.13) + (.36n-.18+.90) = 2.60
Add all the n values first, then do all the addition/subtraction to come up with
.67n + .59 = 2.60
Subtract .59 from both sides
.67n = 2.01
Divide both sides by .67
n = 3
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So to check answers, go back to original values above
5 cent stamp = n * There are 3 of these which equal .15
13 cent stamp = 2n-1 *There are 5 of these which equal .65
18 cent stamp = 2n-1+5 *There are 10 of these which equal 1.80
Add them together .15 + .65 + 1.80 = 2.60

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