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How many 8 digit numbers r there?
Thr r nnt mlln ght dgt nmbrs.
What 3 digit number multiplied by a 2 digit number equals a four digit number and you must use all numbers 1 through 9?
I think you r cheating Mr.Cheater
How many seven digits number can be made from numbers 123456789 but no repititions are allowed?
181440 possible numbers. 9 choices for first digit, leaving 8 choices for the second digit for each of these choices for the first digit, leaving 7 choices for the third digit for each of these choices for the second digit, leaving ... 3 choices for the seventh digit for each of these choices for the sixth digit, giving 9 x 8 x 7 x ... x 3 = 181440 possible numbers. More generally, when there are n different items and r need to be selected from them in order it is called a permutation and the number of ways of doing this is: nPr = n!/(n-r)! where the exclamation mark means "factorial" which is the product of all numbers from 1 to the number, that is n! = n x (n-1) x (n-) x ... x 2 x 1. In this case, there are n=9 items and r=7 need to be selected giving: 9P3 = 9!/2! = 9 x 8 x ... x 3 = 18144
If using numbers 1 thru 49 how many 6 digit combinations can be made?
Using the formula n!/r!(n-r)! where n is the number of possible numbers and r is the number of numbers chosen, there are 13983816 combinations of six numbers between 1 and 49 inclusive.
How many combinations of 9 if you had to use all 9?
Applying the formula n!/(n - r)! to the numbers n = 9 and r = 9, where n is the number of numbers to choose from, and r is the number of numbers chosen, 9! / (9 - 9)! is equal to 9 factorial. This is equal to 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 = 362880 combinations.
