An estimated 3 out of every 25 men are left-handed.

I'm not sure what your question here is, but I am assuming you want to find percentage of the men that are left handed. If I am wrong, just comment below what is your real answer.

For every 25 men, 3 of them are left handed. If we divide 3 by 25, we will get our percentage.

3 / 25 = 0.12

Then move the decimal point two places to the right and make into a % sign.

0.12 = 12%

So, 12% of men are left handed out of the 25 men.

You want to isolate your variable.