Question

Find the sum of all 3-digit natural no. Which are divisible by 13

Answer 1

Hello mate......

Here is your answer↡↡↡↡↡↡↡↡

All 3- digit natural numbers, which are divisible by 13 are 104+117+130+......+988.

Here a= 104 and d= 13

Tn = 988.
a+ (n- 1)× d = 988
104 + (n-1)×13 = 988

(n-1)×13 = 988-104

(n-1)×13 = 884

n-1 = 68

n = 69.

Sn = n ÷ 2 × ( 104+988 )

= 69 ÷ 2 × 1092

= 69× 546

= 37674.

HOPE IT HELPS U......✌✌✌✌✌✌✌

Answer 2

ATQ 

AP: 104 , 117 , 130  ........... 988

a = 104  ,  an =  988

988 = 104 + (n-1) 13

988 - 104  =  (n-1)13 

884 13 = n-1

n= 69

sn= n 2 ( a + an )

Sn = n2 ( 104 + 988)

Sn= 692 ( 1092 )

Sn= 37674

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