RBI Grade B Officers 22 Nov 2015 Paper

A, B and C start a business in partnership with respective initial investments of Rs. 4200, Rs. 3600 and Rs. 2400. After 4 months from the start of the business, A invests an additional amount of Rs. 1000 in the business. After 6 months from the start of the business B and C invest additional amounts in the respective ratio of 1 : 2. After 10 months they get a total profit of Rs. 2820. If the share of A in profit be Rs. 1200, what was the additional investment made by B?