The average of some natural numbers is 15. If 30 is added to first number and 5 is subtracted from the last number the average becomes 17.5 then the number of natural number is ?

The average of *n *natural number = 15

New average of *n *natural numbers = 17.5

ATQ,

(17.5) *n *= (15)*n *+ 30 – 5

17.5*n *– 15*n *= 25

*n *= 10

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