Find the total sum of original observations by using the formula of mean. Then, add the difference of 70 and 170 to the orignal sum. Then, find the final mean.

Find the total sum of all 15 observations. Then, find the total of first 8 and last 8 observations.

Think about how much the total of all the observations would increase.

Apply the formula for mean

Think about the steps involved in drawing a frequency polygon.

Think about the basic formula of mean.

Use the formula of mean and find the total sum of five numbers and then sum of the remaining four numbers.

Think about the total sum of observations for the mean 15 and mean 20.