Question

There are 5 red counters ad y blue counters in a bag. Imogen takes a counter from the bag at random. She puts the counter back into the bag. Imogen then takes another counter at random from the bag. The probability the first counter imogne takes is red and the second counter Imogen takes is red is 1/9 work out how many blue counters there are

Answer 1

Here is a photo of the working out, if you have any questions let me know. The topic for this is called algebraic probability/probability equations if you need more practice.
There are 10 blue counters