Question

The average age of a group of 9 friends as 15 years. If a new person joins that group. The average increase by 21 years. Find the age of new person.

Answer 1

Answer:

Step-by-step explanation:

average=sum /number of persons

let the sum of persons be x

x/9=15

x=135

now a new person has joined the group

then average=sum/number

average=21

so'

21=x+new person/10

x+new person=210

new person=210-135=75 years

Answer 2

Step-by-step explanation:

Average is 15 years therefore total age is

15×9=135 ........(1)

Now,

new friend join then total friends is 10

and average is 21 therefore total age is 21×10=210.......(2)

now,

subtract 1 from 2 to get the age of new friend

210 - 135 = 75

therefore,

the age of new friend is 75 years

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