Question

Two years ago the mean age of 40 people was 11 years .now a person left the group and the mean age is changed to 12 years .find the age of the person who left the group

Answer 1

Solution :

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Given :

Statement 1 :

Two years ago the mean age of 40 people was 11 years .

⇒ So, at present the mean age will be increased by 2,.

Hence, the mean age at present will be 11 + 2 = 13 years,.

Statement 2 :

now a person left the group and the mean age is changed to 12 years,.

⇒ So, the number of people reduced by 1 & the mean changes to 12 years,.

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We know that,

Mean = $\frac{Sum (of) (all) (the) (obeservations)}{total(number)(of)(observations}$

⇒ $\frac{Sum (of) (all) (the) (obeservations)}{40} = 13$

⇒ Sum of all the observations = 40 x 13

⇒ Sum of all the observations = 520

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Let the age of the man be x,

Then,

after he left the group,

⇒ $\frac{520-x}{40-1} = 12$

⇒ 39 x 12 = (520 -x)

⇒ 468 = 520 - x

⇒ x = 520 - 468

⇒ x = 52

   ∴ The age of the person who left the group is 52 years

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                                         Hope it Helps !!

Answer 2

Answer:

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