NECO 2022 · Paper 1 · Q12

Sequences & series (AP, GP)

The 5th and 11th terms of an Arithmetic Progression (A.P.) are 13 and 31 respectively. Find the sum of its first term and common difference.

Worked solution (try it first)

Write the terms: $a + 4d = 13$ and $a + 10d = 31$ .
Subtract: $6d = 18$ , so $d = 3$ .
Then $a = 13 - 12 = 1$ , and $a + d = 1 + 3 = 4$ , option A.

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