Hey Mike, on question #3 page 189 I dont understand how to make the equation with the problem and the explanation didnt help me.

Remember, averages questions are usually about sums. If the average of the first m days is 87 degrees, then the sum of those days must be 87m. The next day it was 93 degrees, so the sum of the first m+1 days is 87m+93.

So far, so good, right?

Now, we also happen to know that the average for those m+1 days was 89 degrees. Just like we did before, we can multiply the average by the number of data points to find the sum: 89(m+1)=89m+89.

Here’s the thing. Both 87m+93 and 89m+89 represent the same sum of the temperatures over the m+1 days. So you can set them equal and solve.

87m+93=89m+89\\87m+4=89m\\4=2m\\2=m

Does that help?

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