Question

Find the sum of all natural numbers from 200 to 700 which are odd and divisible by 7 (From the chapter arthmetic progression)

Answer 1

The Right Answer is 16,128


Solution:-
The odd natural no. divisible by 7 are =
203,217,231,_ _ _ _ _,693.
here, a=203 and d=14
therefore the given sequence is in A.P.

tn =a+(n-1)d
693=203+(n-1)14
693=203+14n-14
693=189+14n
693-189=14n
504÷14=n
36=n

since
Sn=n/2[2a+(n-1)d]
S36=36/2[2×203+(36-1)×14]
S36=18[406+35×14]
S36=18[406+490]
S36=18[896]
S36=16128

Answer 2

hope this will be helpful