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THMETIC PROGRESSIONSFind the 20th term from the last term of the AP: 3,8, 13,. . , 253. |
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Answer» Given series is 3, 8, 13, ...... 253 here, first term , a = 3 common difference , d = 5 Let us find total number of terms at first.use Tn = a+(n-1)d=> 253 = 3 + (n - 1)5 => 250 = 5(n - 1) => n - 1 = 50 => n = 51 so, there are 51 terms in given series.now we know, mth term from last =last term - mth term + 1 so, 20th term from last = 51 - 20 + 1 = 32 hence, 20th from last = 32th term from first use , T32 = a + (32-1)d= 3 + 31 × 5 = 3 + 155 = 158 hence , 20th term from last = 158 Like my answer if you find it useful! |
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