I'm trying to copy a formula.

The worksheet has 10 rows of numbers and I want to find what percentage of
the total each row equals. As my starting formula, I've entered "=A1/A11"
I then copy the formula and paste it into rows 2-10. But what I end up with
are formulas reading "=A1/A12," "=A1/A13," "=A1/A14" and so on.

How do I keep the dividing number constant?

Thanks.