Q4 of 49 Page 105

Which term of the AP : 3, 8, 13, 18, . . . ,is 78?

Given, a = 3, d = a2 – a1 = 8 – 3 = 5, an = 78, n = ?


We know that an = a + (n – 1)d


78 = 3 + (n – 1)5


(n – 1)5 = 78 – 3 = 75


n – 1 = 15


n = 15 + 1 = 16


Thus, 78 is the 16th term of given AP.


More from this chapter

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2

Choose the correct choice in the following and justify:

(i) 30th term of the AP: 10, 7, 4, . . . , is


A. 97 B. 77


C. –77 D. – 87


(ii) 11th term of the AP: is


A. 28 B. 22


C. –38 D. – 48

 3

In the following APs, find the missing terms in the boxes :

(i)


(ii)


(iii)


(iv)


(v)

5

Find the number of terms in each of the following APs :

(i) 7, 13, 19, . . . , 205


(ii)

6

Check whether – 150 is a term of the AP : 11, 8, 5, 2 . . .