Question

Which term of the A.P:- 121, 117, 113,... is 40 less than it's 6th term?​

Answer 1

Step-by-step explanation:

given : a = 121 , d = - 4

to find n for which aₙ = a₆ - 40

now, a₆ = a + 5d

=> 121 + 5(-4)

=> 121 - 20

=> 101

aₙ = a₆ - 40

=> aₙ = 101 - 40

=> aₙ = 61

now 61 = [ a + (n - 1) d ]

=> 61 = [121 + (n - 1) x (-4) ]

=> 61 = [ 121 - 4n + 4 ]

=> 61 = [ 125 - 4n ]

=> 61 - 125 = - 4n

=> - 64 = - 4n

=> n = - 64 / - 4

=> n = 16

therefore 16th term is 40 less than its 6th term