Question

Find the sum of first 20 terms of an AP whose first term is 3 and last term is 57

Answer 1

a=3
a+(n-1)d=57
(n-1)d=54
S20=10 [2a+(n-1)d]=10 (6+54)=10*60=600

Answer 2

Answer:

The answer is 600

Step-by-step explanation:

a=3

n=20

last term = 57

d =??

since, tn = a+(n-1)d

=> 57 = 3 + (n-1)d

=> 57 - 3 = (n-1)d

=>54 = (n-1)d

therefore, Sn = n/2 [2a + (n-1) d ]

=> Sn = 20/2 [2×3 + 54 ] since (n-1)d = 54

=> Sn = 10 [6+54]

=> Sn = 10 × 60

=> Sn = 600 (ans.)

hope it will help uhhh