Banks - Teaser

Solution:- 

Let us assume he buys and goods.

Total CP = 20n

Total SP = 2 + 4 + 6 + 8 ….n terms

Total SP should be at least 40% more than total CP

2 + 4 + 6 + 8 ….n terms ≥ 1.4 * 20 n

2 (1 + 2 + 3 + ….n terms) ≥ 28n

N (n + 1) ≥ 28n

n2 + n ≥ 28n

n2 - 27n ≥ 0

n ≥ 27

He should sell a minimum of 27 goods.