Question

A postal clerk sold some 15 cent stamps and some 25 cent stamps. Altogether 10 stamps were sold for a total cost of 1.70$. How many of each type of stamp were sold?

Answer 1

Explanation:

Let the number of 15 cent stamps be represented by X and

let the number of 25 cent stamps be represented by Y.

The equations would be as follows;

X+Y = 10

0.15X + 0.25Y = 1.70

To get X in terms of Y, use the first equation ; X = 10-Y

Next, replace X in the second equation by 10 -Y

0.15(10-Y) + 0.25Y = 1.70

1.5 -0.15Y +0.25Y = 1.70

Subtract 1.5 from both sides of the equation and sum up the Ys;

0.1Y = 1.70-1.5

0.1Y = 0.2

Divide both sides by 0.1;

Y = 0.2 / 0.1

Y = 2

Replace Y by 2 in any of the first to equations, I'll use X+Y=10;

X+2 =10

X= 8

Therefore, the 15 cents stamps are 8 and 0.25cents stamps are 2