3 times the 10th term is equal to 5 times the 20th term. Find the 20th term.?

Given, 3a10 = 5a20

⇒ 3(a + 9d) = 5(a + 19d)

⇒ 3a + 27d = 5a + 95d

⇒ 3a –5a = 95d – 27d

⇒ –2a = 68d

a = –34d

a20 = a + 19d = –34d + 19d = –15d

As we have only one relation between a and d, so we cannot find the value of a20.

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