A certain alloy contains 5.25% copper. How much copper is there in a piece weighing 200 pounds?

0.0525

The percent sign means divide. So you just move the decimal over two places to the left. To find the percentage, we multiply this 'decimal' form of the percent by 200.

0.0525*200 = 10.5

The 200-pound piece of alloy contains 10-1/2 pounds of copper.