Question

find the sum of all natural numbers between 1605 and 1905 which are not divisible by 6?

Answer 1

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MATHS

The sum of all natural numbers less than 400 which are not divisible by 6 is

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ANSWER

Sum of all natural number less than 400 =

2

1

×399×400=79800

Now the number which are divisible by 6 are in A.P

6,12,18,24,30...396

So here a=6,d=6,a

n

=396

To find the number of terms

a

n

=a+(n−1)d

396=6+(n−1)×6

396=6+6n−6

n=66

Sum of natural number which are divisible by 6.

s

n

=

2

66

×(6+396)

s

n

=66×201=13266

By subtracting sum of natural number from sum of natural number divisible by 6 will get the sum of natural number which not divisible by 6.

Sum of natural number which not divisible by 6 =79800−13266=66534.

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Answer 2

Answer:

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Step-by-step explanation:

s

n

=

2

66

×(6+396)

s

n

=66×201=13266