CBSE Class 10 Answered
an AP has 21 terms. the sum of it's 10th, 11th,12th terms is 129 and the sum of the last three terms is 237. find the AP.
Asked by anukeshd | 09 Mar, 2013, 12:08: AM
Expert Answer
Answer : Given : an AP has 21 terms. the sum of it's 10th, 11th,12th terms is 129 and the sum of the last three terms is 237
To find : AP
Let a and d be the first term and common difference of the given A.P.
a 10 + a 11 + a 12 = 129
=> (a + 9d) + (a + 10d) + (a + 11d) = 129 [an = a + (n – 1)d]
=> 3a + 30d = 129
=> a + 10d = 43 … (1)
a 19 + a 20 + a 21 = 237
=> (a + 18d) + (a + 19d) + (a + 20d) = 237
=> 3a + 57d = 237
=> a + 19d = 79 … (2)
Solving (1) and (2), we get
a + 19d – a – 10d = 79 – 43
=> 9d = 36
=> d = 4
When d = 4, we get
a + 10 * 4 = 43
=> a = 43 – 40 = 3
Thus, the given A.P. is 3, 7, 11, 15… Answer
Answered by | 09 Mar, 2013, 12:48: AM
Application Videos
Concept Videos
CBSE 10 - Maths
Asked by purbashadebnath1980 | 09 Mar, 2024, 12:10: PM
ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by deepikaselvam2009 | 20 Feb, 2024, 08:57: PM
ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by keshavsinghalhapur | 16 Jan, 2024, 08:46: PM
ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by keshavsinghalhapur | 15 Jan, 2024, 10:56: AM
ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by durgauikey7000 | 08 Dec, 2023, 08:16: PM
ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by skandachiranjeevin | 06 Dec, 2023, 07:08: PM
ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by shaikhyakub9946 | 30 Nov, 2023, 11:50: AM
ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by prassanna.j | 13 Nov, 2023, 11:24: PM
ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by prassanna.j | 13 Nov, 2023, 11:23: PM
ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by latayadav23 | 17 Oct, 2023, 08:39: PM
ANSWERED BY EXPERT