Question

If 12th term of an ap is -13 and sum of 1st four term is 24. What is the sum of first 20 terms

Answer 1

-200

Explanation:

ATQ, a+11d=-13 and a+a+d+a+2d+a+3d=24, 4a+6d=24. Solving this, we get a=9 and d=-2. Sum of the first 20 terms is 10*(18+(19)*(-2))=-200