Question

If the mean of five consecutive natural
numbers is 20, find the value of the first
number when it is multiplied by 5.​

Answer 1

Mean of 5 consecutive natural numbers = 20

Let first natural number = x

( x + 1 ), ( x + 2 ), ( x + 3 ), ( x + 4 ) are the second, third, forth and fifth numbers respectively.

Mean :

( Sum of all values) / ( Quantity of numbers )

According to the question

⟹ 20 = {(x) + (x + 1) + (x + 2) + (x + 3) + (x + 4) } / 5

⟹ 20 = ( 5x + 1 + 2 + 3 + 4 ) / 5

⟹ 20 = (5x + 10) / 5

⟹ 20 = { 5 ( x + 2) } / 5

⟹ 20 = x + 2

⟹ 20 - 2 = x

⟹ 18 = x

First Number = x = 18

The value of first number when multiplied by 5 :

⟹ 18 × 5

⟹ 90

Answer 2

Answer:

Mean of five consecutive natural numbers is = 20

Let the first number be = x

Solution:-

So the first five consecutive natural numbers are:-

(x), (x+1), (x+2), (x+3), (x+4)

As follows:-

→ 20 = { (x), (x+1), (x+2), (x+3), (x+4)} ÷ 5

→ 20 = {(5x +1 +2 +3 +4)} ÷ 5

→ 20 = (5x + 10) ÷ 5

→ 20 = {5x ( x + 2)}

→ 20 = x + 2

→ x = 20 - 2

Ans:- 18

So the first number is 18

So when we multiply the first number by 5:-

= 18 × 5

= 90

So the final answer is 90