In how many ways can Alok choose 15 colours from a box of 25 colours such that red, yellow, green, blue must always be included?
Note the following:
The formula for the combination for the selection of the items from the
different items is
The restricted combination for the selection of the items from the
different items with
particular things always included is
Since 4 colours must always be included, the following is evident.
The number from which the restricted combination is to be made is
.
The number with which the restricted combination is to be made is
Therefore, the required restricted combination is
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