SOLUTION: Sarah and Keith Robinson purchased 40 stamps, a mixture of 39 cent and 24 cent stamps. Find the number of each type of stamp if they spent $14.85

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Question 518241: Sarah and Keith Robinson purchased 40 stamps, a mixture of 39 cent and 24 cent stamps. Find the number of each type of stamp if they spent $14.85
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = number of 39c stamps
Let +b+ = number of 24c stamps
given:
(1) +a+%2B+b+=+40+
(2) +39a+%2B+24b+=+1485+ ( in cents )
Multiply both sides of (1) by 24
and subtract (1) from (2)
(2) +39a+%2B+24b+=+1485+
(1) +-24a+-+24b+=+-960+
+15a+=+525+
+a+=+35+
and, since
(1) +a+%2B+b+=+40+
(1) +b+=+40+-+35+
(1) +b+=+5+
They buy 35 39c stamps
They buy 5 24c stamps
check:
(2) +39%2A35+%2B+24%2A5+=+1485+
(2) +1365+%2B+120+=+1485+
(2) +1485+=+1485+
OK