A bag has 3 red balls and 5 green balls. I take out 2 balls, without replacing them. What is the probability of choosing at least one red ball? Give your answer to 3 decimal places.
Student would likely draw a tree diagram to represent the different outcomes. They should recognise that you must add the probability of choosing only one red ball, and two red balls. The outcomes are:Green then Red, Red then Green, Red then Red.Green then Red: (5/8)(3/7). Red then Green: (3/8)(5/7). Red then Red: (3/8)*(2/7)Summing these gives a probability of 36/57.This gives 0.632 to 3 decimal places.
JG
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