0 Deepak Bora Asked: July 14, 20202020-07-14T23:21:08+05:30 2020-07-14T23:21:08+05:30In: CBSE Which term of the A.P. 3, 8, 13, 18, … is 78? 0 In this question the last term of A.P. is given, you have to find which term of A.P. this must be. This is question number 4 exercise 5.2,NCERT Maths solutions. a.p formulaarithmetic progressionnth term Share Facebook Related Questions In an AP the first term is 2, the last term is 29 and sum of the terms ... In an AP the first term is 22, nth term is -11 and sum to first nth terms ... The first and last terms of an AP are 4 and 81 respectively. If the common difference is ... The sum of the first 9 terms of an AP is 81 and the sum of its first ... If the sum of first 7 terms of an AP is 49 and that of first 17 terms ... 1 Answer Voted Oldest Recent Deepak Bora 2020-09-22T14:59:51+05:30Added an answer on September 22, 2020 at 2:59 pm Solution: 11th term, a_{11} = 38 and 16th term, a_{16} = 73 We know , a_{n} = a + (n−1)d a_{11} = a + (11−1)d 38 = a + 10d ………………………………. (i) By the same way, a_{16} = a +(16−1)d 73 = a+15d ………………………………………… (ii) On subtracting eq. (i) from (ii), 35 = 5d d = 7 From eq. (i), 38 = a+10×(7) 38 − 70 = a a = −32 a_{31} = a +(31−1) d = − 32 + 30 (7) = − 32 + 210 = 178 So, 31st term is 178. 0 Reply Share Share Share on Facebook Share on Twitter Share on LinkedIn Share on WhatsApp Leave an answerLeave an answerCancel reply Featured image Select file Browse Add a Video to describe the problem better. Video type Youtube Vimeo Dailymotion Facebook Choose from here the video type. Video ID Put Video ID here: https://www.youtube.com/watch?v=sdUUx5FdySs Ex: "sdUUx5FdySs". Click on image to update the captcha. Save my name, email, and website in this browser for the next time I comment.

Solution:11th term, a

_{11}= 38and 16th term, a

_{16}= 73We know ,

a

_{n}= a + (n−1)da

_{11}= a + (11−1)d38 = a + 10d ……………………………….

(i)By the same way,

a_{16}=a+(16−1)d73 =

a+15d…………………………………………(ii)On subtracting eq.

(i)from(ii),35 = 5

dd= 7From eq.

(i),38 =

a+10×(7)38 − 70 = a

a = −32

a

_{31}= a +(31−1) d= − 32 + 30 (7)

= − 32 + 210

= 178

So, 31st term is 178.