Q22 of 202 Page 9

Find n if the given value of x is the nth term of the given A.P.

(i)


(ii)


(iii)


(iv)

(i)

a = 25, d = 50 – 25 = 25


Last term, l = 1000


Number of terms, n = + 1


= + 1 = 40


Hence, the value of n is 40


(ii)


a = -1, d = -2


Last term, l = -151


Number of terms, n = + 1


= + 1 = 76


Hence, the value of n is 76


(iii)


a = , d =


Last term, l = 550


l = a + (n – 1) d


550 = + (n – 1)


550 =


1100 = 11n


n = 100


Hence, number of terms, n = 100


(iv)


a = 1, d = – 1 =


Last term, l =


a + (n – 1) d =


1 + (n – 1) =


= – 1 +


=


10n = 170


n = 17


Hence, value of n is 17


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