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 the first and the last terms of an A.P. are 7 and 49 respectively.
Also sum of all its terms is 420
Now we have to find the common difference
CBSE DHANPAT RAI publication
CBSE Mathematics Class 10th
Question 26
Given A.P. has first term(a) = 7, last term(an) = 49 and sum(Sn) = 420.
Now by using the formula of sum of n terms of an A.P.
Sn = n[a + an] / 2
So,
=> 420 = n[7 + 49]/2
=> 28n = 420
=> n = 15
By using the formula of nth term of an A.P.
an = a + (n – 1)d
So,
=> 49 = 7 + (15 – 1)d
=> 14d = 42
=> d = 3
Hence, the common difference of the given A.P. is 3.