Mia's quiz scores are 90, 84 and 88. What score on the next quiz…

Step by step

The question

Question: Mia's quiz scores are 90, 84 and 88.

What score on the next quiz makes her mean 89?

1 Total needed

After the next quiz there will be 4 scores.

For a mean of 89, the 4 scores must add up to 89 times 4.

That is 356.

The mean times how many numbers gives the total.

That is the key idea today.

Careful!

With the next quiz, there are 4 scores, not 3.

So we multiply by 4.

2 Total so far

Now we add the 3 scores we know, from left to right.

So far, the total is 262.

3 What is missing

The total must go from 262 up to 356.

The missing part is 356 minus 262.

That is 94.

4 Check

Let's check: 262 plus 94 is 356.

And 356 divided by 4 is 89, the mean we wanted.

So it is right!

Let's look back.

First: total needed.

Then: total so far.

Then: what is missing.

Last: check.