How would you solve this equation? (100)-(90+x)=-30

## 3 Answers

By simplifying, combining like terms, then rearranging to isolate x.

Here's the important first step. Remember that when you subtract an expression in parentheses, that multiplies everything inside the parentheses by -1, changing the sign.

Example: 5 - (4 - x) = 5 + (-1)(4 - x) = 5 + (-4) + x = 1 + x

Example: 5 - (2 + x) = 5 + (-1)(2 + x) = 5 + (-2) + (-x) = 3 - x

Do that with your left hand side.
If you multiply the second set of parentheses by -1, so +90 -x, then you just do algebra like normal.  So 100 + 90 - x= -30. 190 - x =-30. -x= -220. -220/-1= 220.
If distributive property is trouble for you, add (90 + x) to both sides.

(100) - (90 + x) + (90 + x) = -30 + (90 + x)

Simplify left side since 100 - b + b means 100.

100 = -30 + 90 + x

Simplify right side by adding -30 and 90.

100 = 60 + x

Now subtract 60 from both sides.

100 - 60 = 60 + x - 60

40 = x

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