The hundreds place cannot be 0 so we have 9 possible numbers fit there. The tens place has 9 options and the units place has 8 options. So there are 9×9×8 = 648 numbers between 100 and 1000 that have distinct digits in them.
A 9-digit number has a property that the first 'n' digits are divisible by 'n'. There is no '0' in the number and all the digits in the number are distinct. What is the number?
625 is a square number because it is 25 times 25 (a number times itself). Find two square numbers, each of which uses all three digits 1, 9 and 6.
