Given: The given series is 20+22+24+26+……….+60 Formula: Sum of first n even numbers =n(n+1) Calculation: 20+22+24+26+…………….+60 ⇒ (2+4+6+……..+60)–(2+4+6+………..+18) ⇒ (30×31)–(9×10) ⇒ 840 Alternate Solution Last term = First term + (n - 1) × Common difference ⇒ 60=20+(n–1)2 ⇒ n = 21 Now, Sum of n terms in AP =