Final answer:
Joe's rate of doing pushups increased by 75% after two weeks of practice. This is calculated by finding the difference between the new and original number of pushups, dividing by the original number, and then multiplying by 100 to get the percent increase.
Step-by-step explanation:
When Joe started his exercise program, he could do 12 pushups in a minute. After practicing for two weeks, he could do 21 pushups in a minute. To find out by what percentage Joe's rate of doing pushups increased, we first calculate the difference between the new amount and the original amount, and then divide that by the original amount and multiply by 100 to convert it to a percentage.
The increase in pushups is 21 - 12 = 9 pushups. To find the percent increase, divide the increase by the original amount: 9 pushups ÷ 12 pushups = 0.75. Finally, multiply by 100 to get the percentage: 0.75 × 100 = 75%.
Therefore, Joe's rate of doing pushups increased by 75%, which corresponds to option (E).