Question

A drawer contains 15 cents stamps and 18 cent stamps the number of 15 cent stamps is four less that three times the number of 18 cent stamps the total value of all the stamps is 1.29 dollars . How many 15 cent stamps are in the drawer

Answer 1

Explanation:

step 1. convert the total value into pennies, so $1.29 = 129 cents

step 2. let x = number of 18 cent stamps

step 3. then, the number of 15 cent stamps will be 3x - 4

step 4. our equation will be 18x + 15(3x - 4) = 129

step 5. expanding, we get 18x + 45x - 60 = 129

step 6. combining, we get 63x = 189

step 7. solving, x = 3 then number of 18 cent stamps

step 8. then 3x - 4 = 9 - 4 = 5 the number of 15 cent stamps

Proof: (18 x 3) + (15 x 5) = 54 + 75 = 129

Answer 2

Answer: there are 5 15 cents stamps in the drawer.

Explanation:

The drawer contains 15 cents stamps and 18 cent stamps.

Let x represent the number of 15 cents stamps that is inside the drawer.

Let y represent the number of 18 cents stamps that is inside the drawer.

the number of 15 cent stamps is four less than three times the number of 18 cent stamps. This means that

x = 3y - 4

The total value of all the stamps is 1.29 dollars. Converting 1.29 dollars to cents, it becomes 1.29×100 = 129 cents.

Therefore

15x + 18y = 129 - - - - - - - - - - -1

Substituting x = 3y - 4 into equation 1, it becomes

15(3y - 4) + 18y = 129

45y - 60 + 18y = 129

45y + 18y = 129 + 60

63y = 189

y = 189/63 = 3

substituting y = 3 into x = 3y - 4, it becomes

x = 3×3 - 4 = 9-4 = 5