Q9 of 48 Page 125

The mean of 35 observations is 20, out of which mean of first 18 observations is 15and mean of last 18 observation is 25. Find the 18th observation.

We know that



⇒ Sum of observations = Mean ×Total number of observations


Sum of 35 observations = 20×35=700


Sum of first 18 observations = 15×18=270


Sum of last 18 observations = 25× 18=450


While adding first 18 observations and last 18 observations, we add 18th observation twice so,


18th observation= Sum of first 18 observations + Sum of last 18 observations - Sum of 35 observations


⇒ 18th observation= 270 + 450 – 700 =20


More from this chapter

All 48 →
7

The calculated mean of 50 observations was 80. It was later discovered that observation 19 was recorded by mistake as

91. What was the correct mean?

 8

Following 10 observations are arranged in ascending order as follows.

2, 3, 5, 9, x + 1, x + 3, 14, 16, 19, 20


If the median of the data is 11, find the value of x.

 10

The mean of 5 observations is 50. One of the observations was removed from the data, hence the mean became 45. Find the observation which was removed.

 11

There are 40 students in a class, out of them 15 are boys. The mean of marks obtained by boys is 33 and that for girls is 35. Find out the mean of all students in the class.