1. Calculate the numerator {Number of favourable terms} and the denominator {Total number of terms} separately using the concepts of arrangement, permutation and combination.
2. Be part of the problem : Imagine you are arranging / selecting the items. The action of taking the object and placing it in the relevant position is the key.
If you have to arrange 10 rings in 4 fingers, you have to imagine yourself picking a ring and placing it on a finger instead of computing the number of rings each finger has.
3. When two or more items are picked it is easier to compute the probability of picking one element at a time than computing the probability of picking many items at a time.
4. When A and B are selected relate the respective probabilities with multiplication. When either A or B is selected relate the respective probabilities with addition.
5. When there are multiple outcomes possible the probability of at-least one of them happening is computed by calculating the reverse probability
= 1 – probability of event not happening.
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