Sum of numbers
Number Theory
Level
pending
Find the sum of all distinct four digit numbers that can be formed using the digits 1,2,3,4,5, each digit appearing at most once.
The answer is 399960.
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1 solution
The answer is 399960. For each x∈{1,2,3,4,5}, there are 4! such numbers whose last digit is x. Thus the digits in the unit place of all the 120 numbers add up to 4!(1+2+3+4+5). Similarly the numbers at ten's place add up to 366 and so on. Thus the sum is 360(1+10+100+1000)=399960