# Trevor needs a 93 on his second quiz to have a quiz average of 90. What score did Trevor receive on his first quiz?

May 16, 2018

87

#### Explanation:

The average of his score can be given by: $\frac{93 + \text{his first quiz mark}}{2} = 90$

$93 + \text{his first quiz mark} = 90 \times 2$

$93 + \text{his first quiz mark} = 180$

$\text{his first quiz mark} = 180 - 93 = 87$

May 16, 2018

To find the average... we always have to add all the numbers and divide it by the number of the numbers

For example....

Find the average of $5 , 9 , 123$

$137$

Three number added this up... so divide this number by 3 to find average

$\frac{137}{3} = 45. \overline{666}$

Here... $45. \overline{666}$ is the average of the three numbers

Back to the question

Let... the first quiz points be $x$

Then total would be $93 + x$

Two numbers would give the average $90$ so....

$\frac{93 + x}{2} = 90$

$93 + x = 180$

color(blue)(x=87