Question

find the 15th of the series 1,4,7,10... what will be the sum of 18 terms?​

Answer 1

Answer:

GIVEN:- A=1 , D=3

TO FIND:- T15 AND S18

SOL:-

Tn = a + (n-1) d [formula]

T15 = 1 + (15-1) 3

T15 = 1 + 14 × 3

T15 = 1 + 42

T15 = 43

NOW,

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

S18 = 18/2 [ 2×1 + (18-1) 3]

S18 = 9 [2+ 17 × 3]

S18 = 9 [2+51]

S18 = 9 × 53

S18 = 477

ANS:- THEREFORE,THE 15TH TERM ON THE SERIES IS 43 AND SUM OF 18 TERMS IS 477