Question

the mean of 35 observation is 20 out of which mean of first 18 observations os 15 and mean of last 18 observations is 25. find the 18th observations

Answer 1

20 is the answer of the 18th observation . the above is the solution

Answer 2

Answer:

18th observation is 20.

Step-by-step explanation:

Given the mean of 35 observation is 20 out of which mean of first 18 observations of 15 and mean of last 18 observations is 25.

we have to find the 18th observations.

Let the sum of total observation be x

The sum of first 18 observation be a

The sum of last 18 observation be b

$\text{Mean of 35 observation =}\frac{\text{Sum of observation}}{\text{Total number of observation}}$

⇒ $20=\frac{x}{35}$  ⇒ x=700

$\text{Mean of first 18 observation =}\frac{\text{Sum of observation}}{\text{Total number of observation}}$

⇒ $15=\frac{a}{18}$  ⇒ a=270

$\text{Mean of last 18 observation =}\frac{\text{Sum of observation}}{\text{Total number of observation}}$

⇒ $25=\frac{b}{18}$  ⇒ b=450

18th observation=(sum of first 15 observation)+(sum of last 15 observation)-(total number of observations)

                           =a+b-x=270+450-700=20

Hence, 18th observation is 20.