Mathematics

Find the 20th term from the last term of the AP : 3, 8, 13, . . ., 253.

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Given,

A.P. : 3, 8, 13, ……, 253.

Reversing the A.P. : 253, ………., 13, 8, 3.

In above A.P.,

First term (a) = 253 and Common difference (d) = 3 - 8 = -5.

20th term = a₂₀

= a + (20 - 1)d

= 253 + 19 × (-5)

= 253 - 95

= 158.

Hence, 20th term from the last term of the AP : 3, 8, 13, . . ., 253 is 158.

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