How_To_Be_Good_At_Math

ALGEBRA • SOLVING EQUATIONS 305

b + 25 = 46

Rearranging equations

Finding the value of a variable is harder if

the variable is mixed with other terms on one

side of an equation. When this happens, we

need to rearrange the equation so that the

variable is by itself on one side of the equals

sign. The key to solving the equation is to

make sure it always balances.

Whatever we do to one side

of the equation, we must do

the same on the other side.

Variable

The variable is now the

subject of the equation

Let’s look at this equation. We can

solve it in simple stages so that we

can isolate the letter b and find its value.

Start by subtracting 25 from both sides

and rewrite the equation. We know

that 25 minus 25 equals zero. We say that

the two 25s cancel each other out.

We are left with the letter b on one

side of the equals sign. We can now

find its value by working out the calculation

on the right of the equals sign.

When we work out 46 − 25, we are

left with 21. So, the value of b is 21.

b = 21

b + 25 − 25 = 46 − 25

b = 46 − 25

42 = 6 × 7 = ÷ 3

73 + b = 105 i − 34 = 19

Missing values

Can you simplify these equations

to find the missing values?

We can check our answer by substituting

21 for the letter in the original equation. 21 + 25 = 46

Both sides of the

equation balance

Answers on page 320

25 and −25 cancel

each other out

TRY IT OUT

304-305_Solving_Simple-Equations.indd 305 29/02/2016 18:57