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| 1. |
Find the 20th term from the last term of the AP : 3,8,13, . . ., 253 |
| Answer» Given series is 3, 8, 13, ...... 253here, first term , a = 3common difference , d = 5Let us find total number of terms at first.use an = a+(n-1)d}⇒ 253 = 3 + (n - 1)5⇒ 250 = 5(n - 1)⇒ n - 1 = 50⇒ n = 51so, there are 51 terms in given series.now we know, mth term from last =last term - mth term + 1so, 20th term from last = 51 - 20 + 1 = 32hence, 20th from last = 32th term from firstuse , a32=a+(32-1)d}= 3 + 31 × 5= 3 + 155= 158hence , 20th term from last = 158 | |