A math instructor has 47 calculators in her office. Of them, 24 have dead batteries, 24 have cracked displays, and 20 have missing buttons. Of those with dead batteries, 10 have cracked displays and 10 have missing buttons. Of those with cracked displays, 10 have missing buttons. There are 2 with dead batteries, cracked displays, and missing buttons. How many calculators does she have with missing buttons as the only defect? (A) 4 (В) 3 (С) 2 (D) 8 (E) 6 (F) 5 (G) 9 (H) 7
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.
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