Question

find number of terms in the AP 2,5,8 ...........119​

Answer 1

Given:

• 2,5,8,...........,119 are in AP
• Number of terms, n=?

Formula:

tn=a+(n-1)d

Solution:

From the given, we get

• a = 2 - - - - >(1)
• a + d = 5 - - - - >(2)

Sub a=2 in eq (2)

(2) => 2+d=5

d=5-2

d=3

• Last term, tn = 119

To find n

Sub a=2, d=3, tn=119 in the formula

tn = a + (n-1)d

119 = 2 + (n-1)3

119 = 2 + 3n - 3

119 = 3n - 1

3n = 119 + 1

3n = 120

n = 120/3

n = 40

Hope this solution will solve your problem