Given: The given series is 20+22+24+26+⋯+60Formula: 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) ⇒ 840Alternate Solution Last term = First term + (n - 1) × Common difference ⇒ 60=20+(n−1)2 ⇒ n = 21 Now, Sum of n terms in AP = 2n(a+l)=221×(20+60)=21×40=840.