Question

find the sum all three digit number which are multiple of 7​

Answer 1

Step-by-step explanation:

3 digit multiples of 7

Smallest number

15×7=105

16× 7=112

17×7=119

22×7 =154

23×7=161

Common difference is 7

Smallest 3 digit number multiple of 7is 105 1 st term

Last term =142×7=994

And the largest one is 994

To find tn

tn= a+(n-1)d

tn =105+7(n-1) =994

( n-1)= (994-105)/7 =889/7 =127

n=27+1=128

Tn =128=994

To find sn

Sn =n/2 [2a+(n-1)d]

Sn= 128/2 [ 2×105+ 127×7]

S128 = 64× [210+889] =64×1089 =69696

The sum of all three digits of multiples of 7 is 69696