Posted by Miranda on Thursday, May 31, 2012 at 12:23am.
Let's new = x, old = y
x+y = 45
x= y+17
y+17+y = 45
2y+17 = 45
2y+17-17=45- 17
2y = 28
2y/2 = 28/2
y = 14
x = y+17
x = 14+17
x = 31
So new tire cost $ 31 and used tire cost $ 14
Let's new = x, old = y
x+y = 45
x= y+17
y+17+y = 45
2y+17 = 45
2y+17-17=45- 17
2y = 28
2y/2 = 28/2
y = 14
x = y+17
x = 14+17
x = 31
So new tire cost $ 31 and used tire cost $ 14
Short-cut for sum/difference problems:
Whenever the sum and difference of two numbers are both given, the bigger number is (sum+difference)/2, and the smaller number is (sum-difference)/2.
(45+17)/2=31
(45-17)/2=14
Most of the time these problems can be solved without pen and paper.
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