One of the most important and exam oriented question from Chapter name- Arithmetic Progression
Class 10th
Chapter number- 9
Exercise :- 9.6
This type of question has been asked in previous years exams.
In this question we have been given that there be an A.P.
first term a and common difference d.
Also, If an denotes its nth term and Sn is the sum of first n terms,
then we have to find n and Sn,
Where a = 5, d = 3 and an = 50.
CBSE DHANPAT RAI publication
CBSE Mathematics Class 10th
Question 56(i)
Given A.P. has a = 5, d = 3 and an = 50.
By using the formula of nth term of an A.P.
an = a + (n – 1)d
So,
=> 50 = 5 + (n – 1)3
=> 3(n – 1) = 45
=> n – 1 = 15
=> n = 16
Now by using the formula of sum of n terms of an A.P.
Sn = n[a + an] / 2
So,
S16 = 16[5 + 50] / 2
= 8[55]
= 440
Hence, the value of n is 16 and sum is 440.