Question

Sum of even numbers from 2 to 198 and sum of odd numbers 1 to 199

Answer 1

For sum of even numbers from 2 to 198,
a= 2
d = 2
an = 198
an = a + (n-1)d
198 = 2 + 2(n+1)
2(n-1) = 196
n-1 = 98
n = 99
So,
Sn= n(a+l)/2
= 99(2+198)/2
= 99 (200)/2
= 99×100
= 9900
For sum of odd numbers from 1-199,
a= 1
d = 2
an = 199
an = a + (n-1)d
199 = 1 + 2(n+1)
2(n-1) = 198
n-1 = 99
n = 100
So,
Sn= n(a+l)/2
= 100(1+199)/2
=100 (200)/2
= 100×100
= 10000
Hope it may help you !!!!!

Answer 2

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