In Example 4 we showed that a true–false test consist-ing of 20 questions can be marked in 1,048,576 different ways. In how many ways can each question be markedtrue or false so that(a) 7 are right and 13 are wrong;(b) 10 are right and 10 are wrong;(c) at least 17 are right?
Permutations and Combinations
If there are 5 dishes, they can be relished in any order at a time. In permutation, it should be in a particular order. In combination, the order does not matter. Take 3 letters a, b, and c. The possible ways of pairing any two letters are ab, bc, ac, ba, cb and ca. It is in a particular order. So, this can be called the permutation of a, b, and c. But if the order does not matter then ab is the same as ba. Similarly, bc is the same as cb and ac is the same as ca. Here the list has ab, bc, and ac alone. This can be called the combination of a, b, and c.
Counting Theory
The fundamental counting principle is a rule that is used to count the total number of possible outcomes in a given situation.
ing of 20 questions can be marked in 1,048,576 different
true or false so that(a) 7 are right and 13 are wrong;
(b) 10 are right and 10 are wrong;
(c) at least 17 are right?
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