A backpack normally costs 25 dollars but it is on sale for 21 dollars. What percentage is the discount?
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You wan't to get it into a format of (x+a)(x+b)=0
where a+b = 3 (the one from the 3x)
and where a*b= -4 (from the last -4)
(x+4)(x-1)=0
See how 4+(-1) = 3 and (4)(-1) = -4
now find what values of x would make the equation equal 0
x=-4
(-4+4)(-4-1) = (0)(-5) = 0
x=1
(1+4)(1-1) = (5)(0) = 0