Question

Sum of all 2 digit natural numbers which are divisible by 7 is

Answer 1

Hey mate..
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Let , the two-digit no. divisible by 7 be n

The list of two-digit numbers divisible by 7 are as follows:--

14 , 21 , 28.......98

SInce,

a2 - a1 = a3 - a2

Therefore,

The list of numbers are in AP.

i.e. AP: 14, 21 , 28 .....98

Here ,

First term, a = 14

Common Difference, d = a2 - a1 = ( 21 - 14 ) = 7

Last term , L = 98

Now,

We know,

L = a + ( n - 1 ) d

=> 98 = 14 + ( n - 1 ) 7

=> 98 = 14 + 7n - 7

=> 98 = 7 + 7n

=> 98 / 7 = 1 + n

=> 14 = 1 + n

=> n = 13

Now,

S(n) = n/2 ( a + L )

= 13/2 ( 14 + 98 )

= 13 × 56

= 728 // Ans.

Hope it helps !!

Answer 2

Answer:

Here is your answers:

Hope it will help you