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).