Question

A brick staircase has a total of 30 steps. The bottom step requires 100 bricks. Each successive step requires two bricks less than the previous step

How many bricks are required for the top most step?

Answer 1

100 + 98 + 96 + 94 + … 30 steps.

Here

a = 100

d = – 2

n = 30

t_n = a + (n – 1)d

t₃₀ = a + (n – 1)d

= 100 + 29 × -2

= 100 – 58

= 42

No. of bricks required for the top step are 42.