AMIT = 12k
and investment of Brijesh = 11K
Let Brijesh invested the money for N months.
Then,
Amit's investment : Brijesh's investment
= (12k X 11) : (11k x N) = 132k : 11kN = 12 : N
12/N = 4/1 [ ∵ ratio of PROFIT is 4 : 1]
4N = 12
N = 12/4 = 3 months
Clearly, Brijesh invested money for 3 months.