SOLUTION: Nine tines Mary's number minus 7 times Peter's number equals 20, and 10 times Mary's number minus 7 times Peter's number equals 30. What are their numbers?
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Question 1060111: Nine tines Mary's number minus 7 times Peter's number equals 20, and 10 times Mary's number minus 7 times Peter's number equals 30. What are their numbers? Answer by Cromlix(4381) (Show Source):
You can put this solution on YOUR website! Hi there,
Make Mary's number = x
Peter's number = y
Nine tines Mary's number minus 7 times Peter's number equals 20
9x - 10y = 20.....Eq(1)
10 times Mary's number minus 7 times Peter's number equals 30.
10x - 7y = 30.....Eq(2)
..........
9x - 10y = 20.....Eq(1)
10x - 7y = 30.....Eq(2)
Subtract Eq(1) from Eq(2)
x = 10
Substitute x = 10 into Eq(1)
9x - 10y = 20
9(10) - 10y = 20
90 - 10y = 20
-10y = 20 - 90
-10y = -70
10y = 70
y = 7
Mary's number is 10
Peter's number is 7
Hope this helps :-)
