Question

Find the sum of numbers from 50 to 120 which are divisible by 7

Answer 1

the ap is 56,63,-----------------119.
a=56
d=7
an=119
n=?
First we have to find the number of terms, we know that
an=(a+(n-1)d)
=119=56+(n-1)7
=119-56=7n-7
=63=7n-7
=63+7=7n
=70=7n
=70/7=n
n=10

The number of terms are 10
Sn=n/2(a+an)
Sn=10/2 (56+119)
=5*175
=875
The sum of the ap is 875....
HOPE this will help you....^--^

Answer 2

the first no. divisible with 7 after 50 is 56 and the last no. before 120 is 119 so we have an AP 
56,63,.....119
a= 56  d=7
first we need to find the no of terms 
An= 56+(n-1)d
= 56+(n-1)7
119-56=(n-1)7
63/7=n-1
10=n
so we have ten such terms 
now,

Sn= 10/2(2(56)+(9)(7))
Sn=10/2(112+63)
Sn=1750/2
Sn=875

thus, the sum of numbers is 875 
HOPE MY ANSWER HELPS AND
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