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Rd Chapter 9 Arithmetic Progressions Ex 9.6 Solutions

Question - 41 : - The sum of first n terms of an A.P. is 3n2 + 4n. Find the 25th term of this A.P. [CBSE 2013]

Answer - 41 : - Let a be the first term and d be common difference

Question - 42 : - The sum of first n terms of an A.P. is 5n2 + 3n. If its mth term is 168, find the value of m. Also, find the 20th term of this A.P. [CBSE 2013]

Answer - 42 : -


Question - 43 : - The sum of first q terms of an A.P. is 63q – 3q2. If its pth term is -60, find the value of p, Also, find the 11th term of this A.P. [CBSE 2013]

Answer - 43 : -


Question - 44 : - The sum of first m terms of an A.P. is 4m2 – m. If its nth term is 107, find the value of n. Also, find the 21st term of this A.P. [CBSE 2013]

Answer - 44 : -


Question - 45 : - If the sum of the first n terms of an A.P. is 4n – n2, what is the first term ? What is the sum of first two terms ? What is the second term ? Similarly, find the third, the tenth and the nth terms. [NCERT]

Answer - 45 : -


Question - 46 : - If the sum of first n terms of an A.P. is 1/2 (3n2 + 7n), then find its nth term. Hence write its 20th term. [CBSE 2015]

Answer - 46 : -


Question - 47 : - In an A.P., the sum of first n terms is (3n2/2)+(13/2)n. Find its 25th term. [CBSE 2006C]

Answer - 47 : -


a25 = 8 + (25 – 1) x 3 = 8 + 24 x 3 = 8 + 72 = 80
Hence 25th term = 80

Question - 48 : - Find the sum of all natural numbers between 1 and 100, which are divisible by 3.

Answer - 48 : -


Question - 49 : - Find the sum of first n odd natural numbers.

Answer - 49 : -


Question - 50 : -
Find the sum of all odd numbers between
(i) 0 and 50
(ii) 100 and 200

Answer - 50 : - (i) Odd numbers between 0 and 50 are = 1, 3, 5, 7, …, 49 in which

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