Weekly Maths Problem

This is a try out a number of different answers type question so you need to work it with a number of possible suggestion.

Tommy has some black weights and some silver weights. The black weights are 1 kilogram each, and the silver weights are 9 kilograms each. Tommy has 5 weights altogether, and they weigh 21 kilograms in total. How many of each colour weight does he have?

You can share your answers here on Facebook or with me as I visit during the week. Remember you need to show your workings out to get the maximum points.