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

Think about the formula of mean which can be used in this question.

The whole numbers start from where?

Total numbers are 50. So, we are actually subtracting 53_50 from the sum of 50 terms. We can get the new sum as negative number by using the 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 steps involved in drawing a frequency polygon.

Think about those which we can not be used to represent graphically.

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.

Calculate the total sum of five terms and put it in the formula of mean to calculate the velue of x.

Think about adding all the terms and then using the formula of finding the mean.