If A = {1, 2, 3, 4, ……19, 20}, how many subsets of A are possible such that the product of all the elements of the subset is even?
Question
If A = {1, 2, 3, 4, ……19, 20}, how many subsets of A are possible such that the product of all the elements of the subset is even?
Solution
The problem is asking for the number of subsets of set A where the product of all elements in the subset is even.
A product is even if at least one of its factors is even. Therefore, we need to find subsets that contain at least one even number.
In set A, there are 10 even numbers (2, 4, 6, ..., 20) and 10 odd numbers (1, 3, 5, ..., 19).
The total number of subsets of a set with n elements is 2^n. So, the total number of subsets of set A is 2^20.
However, this includes subsets that only contain odd numbers. The number of such subsets is 2^10, because there are 10 odd numbers in set A.
Therefore, the number of subsets of A that have an even product is the total number of subsets minus the subsets that only contain odd numbers.
So, the answer is 2^20 - 2^10.
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