Question

Mean of 10 observation is 20 if one number is included the mean becomes 21 the included number

Answer 1

the included number is 31

Explanation:

the mean is calculated as

mean =
`(sum)/(count)`

given the mean of 10 observations is 20 , then

`(sum)/(10)` = 20 ( multiply both sides by 10 )

sum = 200

if a number is included , count = 11 and mean = 21

let x be the included number , then

`(200+x)/(11)` = 21 ( multiply both sides by 11 )

200 + x = 231 ( subtract 200 from both sides )

x = 31