After a few hours, David finally arrived at his hotel. When he wanted to open his briefcase; he couldn't remember the 4-digit combination code. He was, however, able to recall:
What is the total number of possible combination code to the briefcase?
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For each digit, find all possibilities.
- 1st digit = 2,3,4,5,6 = 5 numbers;
- 2nd digit = 2,3,5,7 = 4 numbers;
- 3rd digit = 5,6,7,8 = 4 numbers;
- 4th digit = 1,3,5,7,9 = 5 numbers.
And then, multiply them. 5x4x4x5 = 400.