In a royal garden, decorative lamps follow this pattern: Row 1 has 4 lamps, Row 2 has 7 lamps, Row 3 has 10 lamps, with each row having 3 more lamps than the previous row. If this pattern continues for 8 rows, how many lamps are in the 8th row?
Show answer & explanation
Correct answer: B
Explanation
Given:
First row (a) = 4
Common difference (d) = 3
Number of rows (n) = 8
Formula:
Nth term of AP
aₙ = a + (n − 1)d
a₈ = 4 + (8 − 1) × 3
= 4 + 7 × 3
= 4 + 21
= 25