High School

Two arithmetic progressions (APs) have the same common difference. The first term of one AP is -1, and the first term of the other AP is -8. What is the difference between their 4th terms?

Answer :

Answer:

The difference between the 4th term of both series is 7

Step-by-step explanation:

The formula for the nth term of an APS is a + (n - 1)×d

The first term of one of the series = -1

The first term of the other of the series = -8

The fourth term of both series is thus;

4th term first series = -1 + (4 - 1)× d = -1 + 3·d

4th term second series = -8 + (4 - 1)× d = -8 + 3·d

The difference between the 4th term of both series = -1 + 3·d - (-8 + 3·d)

-1 + 3·d - (-8 + 3·d) = -1 + 3·d + 8 - 3·d = 8 - 1 = 7

The difference between the 4th term of both series = 7.