Match the given numbers with their respective number of digits.
0001, 0010, 0100, are not 4-digit numbers. They are one, two & three digit numbers respectively as the zeroes to the left don't change the value of the number and can be ignored.
0001 is a one digit number 1 .
0010 is a two digit number 10 .
0100 is a three digit number 100 .
1000 is a four digit number.