You copy the formula = SUM ($A1:C1) from cell D1 to cell F10. What will the formula change to?

The formula will change to = SUM ($A10:E10)

Explanation:

Look at the difference between = SUM ($A1:C1) and = SUM ($A10:E10).

In both cases column A is present because in the original formula 'A' is next to '$' sign.

In the original formula the row 1 is used because the destination cell, D1, is in row 1; after the copy is made, the destination cell F10 is in row 10, so the '1' is changed to a '10'.

C is changed to E because C column is the previous column to the destination cell, D1, in the original formula and E is the previous column to the destination cell, F10, after the copy.

It will change to = SUM ($A10:E10)

Explanation:

A1 is the first selection of the series, and because you move the series down ten spaces it changes to A10 instead of A1. C1 changes to E10 because the series is again ten spaces below the original cell and over two columns from C to E, since you moved the formula to F10.