Ava's test scores are 88 and 92. What score on the next test makes…

Step by step

The question

Question: Ava's test scores are 88 and 92.

What score on the next test makes her mean 90?

1 Total needed

After the next test there will be 3 scores.

For a mean of 90, the 3 scores must add up to 90 times 3.

That is 270.

The mean times how many numbers gives the total.

That is the key idea today.

Careful!

With the next test, there are 3 scores, not 2.

So we multiply by 3.

2 Total so far

Now we add the 2 scores we know, from left to right.

So far, the total is 180.

3 What is missing

The total must go from 180 up to 270.

The missing part is 270 minus 180.

That is 90.

4 Check

Let's check: 180 plus 90 is 270.

And 270 divided by 3 is 90, 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.