if you have one equation that gives you x or y
use substitution
x+3y=18
x= 18-3y
substitute (18-3y) for x in the other equation
if you have coefficients that will not 'reduce'
use elimination
2x+3y= -3
5x-4y=9
watch for equations that will reduce
2x+4y= -8
divide through by 2
x+2y= -4
x= -4-2y
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sum is addition difference is subtraction
the inverse of addition is subtraction and the inverse of multiplication is division. Of course, multiplication is just repeated addition so division is just repeated subtraction!
What is the difference between 392 and 247?
the difference is also doubled
There is no difference in value between "equal" fractions: the difference is zero.