There are 10 digits from which the first number can be selected, 10 digits from which the second number can be chosen and 10 from which the third number can be picked.
This gives you a total number of combinations of 10 x 10 x 10 = 1000.
How many permutations of 3 different digits are there, chosen from the ten digits 0 to 9 inclusive?
There are 2 digits in 30. They are 3 and 0.
TWO digits are in the number 30, 3 and 0
There are two digits, 3 and 0, in the number 30.
Two significant digits, the 7 and trailing 0.
1000
The are 100,000,000.
The ones column are in single digits and if there are none then the 0 digit is used.
Three significant digits. Any 0's on the left side are excluded from significant digits but 0's on the right side are included.
2 - 0 & 1
1000
There are 3 significant digits in 0.000540 (5, 4 and the final 0).