The smallest five digit number that can be formed by using the digits 9 , 7, 4 ,0 and 1 , each only once, is

As there are only 5 digits available, we have to use all of the digits to form a 5 digit number. To form the smallest number possible using these numbers, the smallest digits should be the first digit of the number and the other digits in an increasing order. But, 0 being the smallest digit here, the number actually becomes a 4 digit numbers in that case. So, we need to put 1 in the first place instead of 0. The arrangement of the digits is 1>0>4>7>9 and so the smallest number is 10479.