How do you work 45 is 20 percent of what number?

To find the number that 45 is 20% of, you can set up a proportion. Let x be the unknown number. The proportion would be: 45/x = 20/100. Cross multiply to solve for x: 45 * 100 = 20x. Simplify the equation to find x: 4500 = 20x. Divide both sides by 20 to solve for x: x = 225. Therefore, 45 is 20% of 225.