SOLUTION: A postal clerk sold some 13 cent stamps and some 20 cent stamps. Altogether, 60 stamps were sold sold for a total cost of $10.25. How many 13 cent stamps were sold?

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Question 188885: A postal clerk sold some 13 cent stamps and some 20 cent stamps. Altogether, 60 stamps were sold sold for a total cost of $10.25. How many 13 cent stamps were sold?
Found 2 solutions by checkley77, jojo14344:
Answer by checkley77(12844) About Me  (Show Source):
You can put this solution on YOUR website!
.13x+.20(60-x)=10.25
.13x+12-.20x=10.25
-.07x=10.25-12
-.07x=-1.75
x=-1.75/.07
x=25 $.13 stamps were sold.
60-25=35 $.20 stamps were sold.
Proof:
.13*25+.20*35=10.25
3.25+7=10.25
10.25=10.25

Answer by jojo14344(1513) About Me  (Show Source):
You can put this solution on YOUR website!


Let x = 13 cent stamps
And y = 20 cent stamps

Then, x + y =60 , Eqn 1

Also, 0.13x + 0.20y = $10.25, Eqn 2

In Eqn 1 you get, y = 60 - x, Eqn 3.
Substitute Eqn 3 in Eqn 2:
0.13x%2B0.20%28highlight%2860-x%29%29=10.25
0.13x%2B12-0.20x=10.25
12-10.25+=+0.20x-0.13x
1.75=0.07x -----> cross%281.75%2925%2Fcross%280.07%29=cross%280.07%29x%2Fcross%280.07%29
highlight%28x=25%29, Number of 13cent stamps ( Answer )

Go back Eqn 3:
y=60-25=red%2835%29, Number of 20 cent stamps

Let's check, go back Eqn 2:
0.13%2825%29+%2B+0.20%2835%29+=10.25
3.25%2B7.00=10.25
10.25=10.25

Thank you,
Jojo