21r-7-r+5=-52 solve for r
2 answers:
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Probability Trees - See linked image
A good visual method for this is a probability tree.
Each set of branches represents the probabilities of on coin being removed, the second set is out of 9 as the first coin is taken and not replaced.
Multiply along the lines to work out the probability of each of the combinations.
*Even though only 'Dime Dime' is needed, it is best to do all of them as this way you are able to get all marks in an exam; you can also add up all the final values as a check to see if you are right.
A good visual method for this is a probability tree.
Each set of branches represents the probabilities of on coin being removed, the second set is out of 9 as the first coin is taken and not replaced.
Multiply along the lines to work out the probability of each of the combinations.
*Even though only 'Dime Dime' is needed, it is best to do all of them as this way you are able to get all marks in an exam; you can also add up all the final values as a check to see if you are right.