Multiple choice

If the 20th term of a sequence is 120 and the common difference of terms is 6, find the first term.

  1. 6

  2. 12

  3. 18

  4. 24
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A Correct answer
Explanation

The n-th term of an arithmetic progression is a + (n-1)d. Given 20th term = 120, n=20, d=6. 120 = a + (20-1)*6. 120 = a + 19*6. 120 = a + 114. a = 6.

AI explanation

Using the formula for the nth term of an arithmetic progression, Tn = a + (n - 1)d, we substitute the known values: 120 = a + (20 - 1)6. Simplifying the equation gives 120 = a + 114. Subtracting 114 from 120 yields the first term as 6.

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