SOLUTION: A stamp collector has some 15 cent stamps and some 20 cent stamps. The number of 15 cent stamps is eight less than three time the number of 20 cent stamps. The total value is $4. F

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Question 201380: A stamp collector has some 15 cent stamps and some 20 cent stamps. The number of 15 cent stamps is eight less than three time the number of 20 cent stamps. The total value is $4. Find the number of each type of stamp in the collection.
Found 2 solutions by Earlsdon, ptaylor:
Answer by Earlsdon(6294) (Show Source):
You can put this solution on YOUR website!
Let x = the number of 15-cent stamps and y = the number of 20-cent stamps.
x($0.15)+y($0.20) = $4.00 and...
x = 3y-8 "The number of 15-cent stamps (x) is eight less than three times the number of 20-cent stamps (3y-8)" Substitute the x here into the first equation and solve for y.
(3y-8)(0.15)+y(0.20) = $4.00 Simplify.
(0.45)y-1.20+(0.20)y = 4.00
(0.65)y-1.20 = 4.00 Add 1.20 to both sides.
(0.65)y = 5.20 Divide both sides by 0.65
y = 8 and x = 3(8)-8 = 16
There are sixteen 15-cent stamps and eight 20-cent stamps.
Check:
16($0.15)+8($0.20) = $2.40+$1.60 = $4.00 OK!

Answer by ptaylor(2198) (Show Source):
You can put this solution on YOUR website!
Let x=number of 20 cent stamps
Then 3x-8=number of 15 cent stamps
we'll deal in pennies
20x+15(3x-8)=400 get rid of parens
20x+45x-120=400 add 120 to each side
20x+45x-120+120=400+120 collect like terms
65x=520 divide each side by 65
x=8--------------------number of 20 cent stamps
3x-8=3*8-8=24-8=16 number of 15 cent stamps
CK
8*20+16*15=400
160+240=400
400=400
Hope this helps---ptaylor