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And another is Sum= n(a+d)/2 where a is the last term and d is the first term.

We can use the first formula where the n is and x is the common difference between any two terms the number of terms, that is xn(n+1)/2

,we can calculate the number of even terms between 1 and 31.See the number of terms between 1 and 30 is 30-1 = 30 terms and to calculate the number of even terms we will divide 30 by 2 which is 15 and the difference between any two even number is 2 , So x=2

So keeping 15 in place of n and 2 in x in the formula xn(n+1)/2

we will get

Sum⇒2×15(15+1)/2

Sum⇒2×15×16/2

Sum⇒15×16

Sum⇒240

Hence, the sum of the even terms between 1 and 31 is

I hope u got want u want !

Plz mark as best!