1. The first space of the code can be filled in 5 ways
the second place in 4 ways, and the third place in 3 ways.
So the number of codes = 5x4x3 = 60
2. So we only have to worry about the last two numbers,
the second last can be filled in 10 ways, (10 numerals), but the last one in only 9 ways, (no zero)
so there are 90 differrent permutations he has to try
and if it takes 20 seconds per try .....
1. how many three-letter code symbols can be formed using a set of 5 different letters in repetion is not allowed?
2. Mark can remember only the first 5 digits of his friends phone number. He also knows that the number has 7 digits and that the last digit is not 0. If mark were to dial all of possible numbers and if takes him 20 seconds to try each one, how long would it take to try every possbility?
Please I need help with this two questions I'm reviewing for my test for next week. Thanks
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then what do I divide 90 by 20? But then I will come up with 4.5 and that is not one of my mult. choice answers.
2 answers