1. Write all possible numbers using the digits 3,6 and 8 without repeating of digits.

Solution:

The numbers are:

3 at unit place: 863,683 | Hint: keep 3 at unit place and interchange the position of 8 and 6 |

6 at unit place:836, 386 |
Hint: keep 6 at unit place and interchange the position of 8 and 3 |

8 at unit place:638,368 |
Hint: keep 8 at unit place and interchange the position of 6 and 3 |

2. How many whole numbers have two digits.

Solution:
The two digits whole numbers are from 10 to 99. e.g. 10,11,12......99.

Therefore the two digit numbers= 99-(10-1)

=99-9

=90

Note:Its general formula is : For two digits number = two digits highest number-(two digits lowest number-1)

3. How many whole numbers have three digits.

Solution:
The two digits whole numbers are from 100 to 999. e.g. 100,101,102......999.

We will apply the same formula by changing the numbers of digits only.

Therefore the three digit numbers= 999-(100-1)

=999-99

=900

Used formula is :three digits highest number-(three digit lowest number-1)

4. What are the greatest and smallest four digits number that can be formed by using the digits 3,0,9,7 without repeating any of the digits in a number?

Solution:
The four digits largest number = the digits in descending orders (9,7,3,0)

=9730

The four digits smallest number = the digits in ascending orders (0,3,7,9) but we have to keep smallest digit 3 at the start to make it four digit smallest number otherwise it will become three digits number if it is started with 0.

=3079

5. Find the difference between smallest 6-digit number and and greatest 5-digit number.

Solution:
The smallest 6-digit number=100000

The greatest 5-digit number=99999

difference= 100000-99999

=1 Ans.