Nora's test scores are 95, 89, 92 and 90. For a mean of 92, what…

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The question

Question: Nora's test scores are 95, 89, 92 and 90.

For a mean of 92, what score does Nora need on the next test?

1 Total needed

After the next test there will be 5 scores.

For a mean of 92, the 5 scores must add up to 92 times 5.

That is 460.

The mean times how many numbers gives the total.

That is the key idea today.

Careful!

With the next test, there are 5 scores, not 4.

So we multiply by 5.

2 Total so far

Now we add the 4 scores we know, from left to right.

So far, the total is 366.

3 What is missing

The total must go from 366 up to 460.

The missing part is 460 minus 366.

That is 94.

4 Check

Let's check: 366 plus 94 is 460.

And 460 divided by 5 is 92, 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.