Given, series is 105+103+101+...+49+47 which is an AP. Here, a=105 and d=103−105=−2 Let nth term =47 ⇒‌‌a+(n−1)d=47 ⇒‌105+(n−1)(−2)‌=47 ⇒‌−2(n−1)‌=47−105 ⇒n−1‌=‌
−58
−2
⇒n‌=29+1 ⇒n‌=30 Hence, number of terms in given series is 30 .