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