Simultaneous equations

Five equations... five unknowns... can you solve the system?

A bag contains red and blue balls. You are told the probabilities of drawing certain combinations of balls. Find how many red and how many blue balls there are in the bag.

Use graphs to gain insights into an area and perimeter problem, or use your knowledge of area and perimeter to gain insights into the graphs...

Investigate the effects of the half-lifes of the isotopes of cobalt on the mass of a mystery lump of the element.