Question

Apostal clerk sold some 15 cent stamps and some 25 cent stamps. Altogether, 15 stamps were sold for atotal cost of $3.15 How many of each type of stamp were sold?

Answer 1

For this case we can define the following notation

x= number of stamps of 15 cents

y= number of stamps of 25 cents

x + y= 15

And we have:

0.15 x + 0.25 y= 3.15

Solving for the first equation we got for x:

y = 15-x

And replacing in the second one we got:

0.15x + 0.25(15-x) = 3.15

0.15x + 3.75 -0.25x =3.15

3.75- 3.15= 0.25x -0.15x

0.6= 0.1x

x = 0.6/0.1= 6

And solving for y we got:

y= 15-6 = 11

So they sold six 15 cent stamps and and eleven 25 cent stamps