Question

Complete the table with the number of sit-ups you have to do sunday so that the mean number of sit-ups per day is 100

Answer 1

The mean is the average of the numbers.

It is easy to calculate: add up all the numbers, then divide by how many numbers there are.

Let the number of sit-ups you have to do Sunday be x. Then the sum of all sit-ups is

100+65+120+150+90+0+x=525+x.

The number of days is 7.

Thus, the mean is

$\text{mean}=\dfrac{525+x}{7}.$

You know that the mean number of sit-ups per day is 100, equate these two means and solve the equation:

$\dfrac{525+x}{7}=100,\\ \\525+x=700,\\ \\x=700-525,\\ \\x=175.$

Answer: 175 sit-ups