A child has three different kinds of chocolates costing Rs.2, Rs.5 and Rs.10. He spends total Rs.120 on the chocolates. What is the minimum possible number of chocolates, he can buy, if there must be at least one chocolate of each kind? 

Given that a child has three different kinds of chocolates costing Rs.2, Rs.5 and Rs.10. 

He spends total Rs.120 on the chocolates

The condition is , child has to buy at least one chocolet from each kind, and he has to buy the minimum number of chocolates

Take 5 chocolets of 2 rupees each, 2 chocoletes of 5 Rupees each, and 10 chocolets of 10 rupees each

The total number of chocolets is $10+2+5=\boxed{\mathbf{17}}$