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One-step Algebra Equations with Addition and Subtraction

In math, an equation means an expression with an equal (“=”) sign.

When we solve an equation we try to find the value of the variable. The expression/value on the left is equal to that on the right.

We follow a method where we separate the variable on one side of the equation using Opposite Operations.

 

How do you solve an equation?

Balance Method to Solve Equations

Add or subtract the same number from both sides to keep the equation in balance.

Solve: x + 8 = 12

Example 1

 + 3 = 8

 x + 3 = 8

     -3 = -3

———————-

                                      x = 5

———————-

Example 2. Solve x + 9 = -12

 

Example 3.  Lily has d watermelons. If she adds 25 to them, it will become 40. Find the value of d.

Equation is d + 25 = 40

-25 = -25

————–

   d = 15

————–

Example 4.  Monica has $x. After shopping for $155 on a sofa, she has only $25. What is the value of x?

Equation is x – 155 = 25

+155 = +155

——————–

                              x = $180

——————–

Example 5. Greg has x no. of books in his office shelf. There are 30 times more books in one of the shelves in the public library. If it’s equal to 4500, how many books does Greg have?

Equation is 30.b = 4500

30.b ÷ 30 = 4500 ÷ 30

                          b = 150

  1. x + 15 = 60

  =  

x   = _____

  1. r – 23 = 49

+ 23 = + 23. Find r.

  1. Max has b number of cars at his taxi service. If he rents out 20, he is left with 25. Find b.

  1. Georgia has n oranges. She adds 12. She is now left with 27. Find n.

  1. Earl has c candies. Mini has 6 times more than what Earl has. If Mini has 36 candies, how many does Earl have?

  1. Mathew has $n in his wallet. He withdraws $200 from an ATM. He has $235 now. What is amount he had earlier?
Answer key
  1. 45
  2. 26
  3. 45
  4. 15
  5. 6 candies
  6. $35

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