If Alma wants to mail a package which requires $1.53 in postage, and has only 5-cent and 8-cent stamps, what is the smallest number of stamps she could use to total exactly $1.53?(a) 24 (b) 23...

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jeew-m's profile pic

Posted on

 Let us say she uses x number of 5-cent and y number of 8-cent stamps.

`0.05x + 0.08y = 1.53`

`x + y = A ` (We want the minimum A)

`A = x + (1.53 – 0.05x) / 0.08 = (1.53 + 0.03x) / 0.08`

Put values for x (whole numbers) until we get a whole number to A

When x = 5 you get A=21.

This is the smallest number.

So the answer is (c)

durbanville's profile pic

Posted on

As we need the least number of stamps to make $1.53 and we need to be exact, calculate how many 8c stamps come closest to the value

`19 times 8c = $1.52` so we can conclude that there are less that 19 stamps of 8c each. 8c stamps < 19

We also need to find a value of 8c stamps that leaves a multiple of 5c stamps so that we can be exact.

So if we use 16 8c stamps, having calculated that neither 18 nor 17 8c stamps leave a multiple of 5

 `16 times 8c =$1.28`  the balance remaining is 25c and 

`5c times 5c = $0.25`   16 + 5 = 21. Option c) is correct.


Therefore c) is the correct answer. 21 stamps are the least number of stamps that can be used to total exactly $1.53

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