A bag has 24 sweet of different colours: 10 red, 8 blue and 6 yellow. What is the probabilty of not getting a blue sweet ?

First the thing you need to know before answering the question is, the probably of not getting something is [ 1 - the probabilty of getting something ], so the probabilty of getting a blue sweet is , the number of blue sweets over total numbers of sweets, so 8/24. The probabilty it is not blue therefore is [ 1 - 8/24 ] so 16/24. But your not finished there. You can see that the 16/24 can be simplified, do devide both the top and bottom by 8, so 2/3. so the probabilty that it is not blue sweet is 2/3 .