First AP
Given a = –1
We know that
an = a + (n – 1) d
So, 4th term will be
a4 = – 1 + (4 – 1) d
a4 = – 1 + 3d
So, 4th term of 1st AP = – 1 + 3d
Second AP
Given b = −8
We know that
bn = b + (n – 1) d
So, 4th term will be
b4 = – 8 + (4 – 1)d
b4 = – 8 + 3d
So, 4th term of 2nd AP = – 8 + 3d
,
So difference between their 4th terms
a4 – b4
= – 1 + 3d – (– 8 + 3d)
= – 1 + 3d + 8 – 3d
= 7
So, the correct answer is (c)

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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