A bag contains 50 p, 25 p and 10 p coins in the ratio 5 : 9 : 4, amounting to Rs.206. Find the number of coins of each type respectively. 

Given that a bag containts 50p, 25p, and 10 paisa coins in the ratio $5:9:4$ amounting to $Rs 206$

The amount is 

  $\begin{array}{rcl}5x\left(50\right)+9x\left(25\right)+4x\left(10\right)& =& 20600\\ 250x+225x+40x& =& 20600\\ 515x& =& 20600\\ x& =& \frac{20600}{515}\\ & =& 40\end{array}$

Therefore, the number of 50 paisa coins is $5·\left(40\right)=\boxed{\mathbf{200}}$, the number of 25 paisa coins is  $9·\left(40\right)=\boxed{\mathbf{360}}$ and the number of 10 paisa coins is $4·\left(40\right)=\boxed{\mathbf{160}}$