
Andrew M. answered 04/03/17
Tutor
New to Wyzant
Mathematics - Algebra a Specialty / F.I.T. Grad - B.S. w/Honors
If Slider is x years old
Changeup is x+4 years ld
x(x+4) = 21
I can see the answer is 3 and 7 years old
but let's finish the algebra:
x2 + 4x = 21
x2 + 4x - 21 = 0
(x+7)(x-3) = 0
x = -7 or x= 3
discarding the negative,
Slider is 3 years old.
Changeup is 3+4 = 7 years old