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You are here: Experts > Science > Math for Kids > Basic Math > Elimination and Substitution
Basic Math - Elimination and Substitution
Expert: Lynn Houston - 11/5/2009
Question
How to solve an equation that has 3 different variables
2a+c=-10
b-c=-15
a-2b+c=-5
Answer
Take the equations with only 2 variable and solve them for a and b, then fill those values into the 3rd equation to solve for c
2a+c = -10 (a = (-10-c)/2))
b-c = -15 (b= c-15)
a-2b+c=-5
(-10-c)/2) - 2(c-15) + c = -5 (multiply everything by 2)
-10-c - 4c + 60 + 2c = -10 (combine like terms)
-3c + 50 = -10
-3c = -60
c = 20 Now you can just fill in the value of c into the 1st and 2nd equations to get the values of a and b
2a + 20 = -10
2a = -30
a = -15
b -20 = - 15
b = 5
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