Question

For the finite A.P. 1, 4, 7, ….. 118. Find the 15th term from the end​

Answer 1

Sol:

1,4,7.....118

Formula:

an = a +(n-1)d

118= 1 +(n-1) 3

118 = 1 + 3n - 3

118 = 3n - 2

118 + 2 = 3n

120 = 3n

$n \: = \frac{120}{3}$

40n

finding last 15 term

40 - 15 = 25

an = 1 + (25 - 1)3

an = 1 + (24) 3

an = 1 + 72

an = 73

this is 25th term so add it with 3

73 + 3

76