Last updated at May 29, 2018 by Teachoo

Transcript

Ex 5.2 ,17 Find the 20th term from the last term of the A.P. 3, 8, 13, , 253 3, 8, 13, .. ,253 Here, a = 3 d = 8 3 = 5 First lets find which term is 253 Let an = 253, a + (n 1) d = 253 Putting values 3 + (n 1) 5 = 253 5(n 1) = 253 3 5(n 1) = 250 (n 1) = 250/5 n 1 = 50 n = 50 + 1 n = 51 We need to find 20th term from the last term Last term = 51st Second last term = 51 1 = 50th Third last term = 51 2 = 49th And so on So, 20th from last term = (51 19)nd term . = 32nd term So, we have to find a32 an = a + (n 1) d Putting values a32 = 3 + (32 1) 5 = 3 + 31 5 = 3 + 155 = 158 So, 20th term from the last term of the given AP is 158

Chapter 5 Class 10 Arithmetic Progressions

Concept wise

- Checking if AP or not and finding a, d
- Finding nth term
- Finding n
- Finding AP
- Finding nth term from end
- Divisible/ multiples
- Statement questions - nth term
- Finding sum of n terms
- Finding number of terms given s
- Given nth term finding s
- Statement questions - Sum of n terms
- Determining AP and finding sum

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.