Exercise 4 Page 155

We want to find how much the store earn on the sale. To do so, we will use the percent equation. part = percent * whole We know that an Val buys a computer for $920, and this is 115 % of what the store paid for the same computer. Let's draw a bar diagram to represent the problem. In the diagram, c will represent the amount the store paid for the computer.

Now we will apply the percent equation to the given situation. For simplicity, we can temporarily ignore the units. part = percent * whole [0.4em] ↓ [0.4em] 920 = 115 % * c We need to write the percent as a decimal before we can solve the equation that we got. To write a percent as a decimal, we will ignore the percent symbol and move the decimal point two places to the left.

Therefore, 115 % is equal to 1.15. 920 = 115 % * c [0.4em] ↓ [0.4em] 920 = 1.15 * c Finally, we will solve the equation for 920.

920=1.15* c

DivEqn

.LHS /1.15.=.RHS /1.15.

920/1.15=1.15c/1.15

CancelCommonFac

Cancel out common factors

920/1.15=1.15c/1.15

SimpQuot

Simplify quotient

920/1.15=c

UseCalc

Use a calculator

800 =c

RearrangeEqn

Rearrange equation

c =800

We got that c= 800 is a solution to the equation. This means that the store paid $800 for the computer Val bought. Finally, we will subtract this price from the amount Val paid for the computer. This way, we will find how much did the store earn. $920- $800=$120