Two friends P and Q started a business investing in the ratio of 5 : 6. R joined them after six months investing an amount equal to that of Q’s. At the end of the year, 20% profit was earned which was equal to Tk. 98000. What was the amount invested by R?

Let the total investment be Tk. z
Then, 20% of z = 98000
⇒ z = 98000 × 100)/20
= 490000.
Let the capitals of P, Q and R be Tk. 5x, Tk. 6x and Tk. 6x respectively.
Then, (5x × 12) + (6x 12) + (6x × 6) = 490000 × 12
⇔ 168x = 490000 × 12 ⇔ x = (490000 × 12)/168 = 35000.
∴ R's investment = 6x = Tk. (6 × 35000)
= Tk. 210000.