math
posted by Alex on .
i need help with this problem x AND y ARE THE SAME IN BOTH PROBLEM????
7x+8y=25
9x+10Y=35

7x+8y=25 times 5 is 35 x + 40 y = 125
9x+10y=35 times 4 is 36 x + 40 y = 140
++++++++++++++++++++++now subtract
1 x + 0 = 15
so
x = 15
then
7(15) + 8 y = 25
105 + 8 y = 25
8 y = 80
y = 10 
thanks but y\why did you multiply it by 4 and 5 at the begging

Because 40 is the least common multiple of 8 and 10
I could have used the first times 9 and the second times 7 and eliminated x. 
What method is this (like is it elimination,substiution)