Question

2017

December
21 Thursday
3
81
Find the 25 tom of AP 5, +11 / 4
3
2.​

Answer 1

Answer:

..............................................

Answer 2

Answer:

Step-by-step explanation:

first term,a=5 , common difference,d=4

Let 81 be the nth term

Tn=a+(n-1)d

81=5+(n-1)4

(n-1)4=76

n-1=19

n=20

Hence 81 is the 20th term

Sn=n/2{2a+(n-1)d}

Sum of the 20 terms = 20/2{2*5+19*4} = 10(10+76) = 860