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In this lesson, we will learn how to count the number of possible outcomes when we have restrictions.

Q1:

Without repeating any of the digits, determine how many four-digit numbers can be formed from 1 , 2 , 3 , 4 , 5 , 6 , and find out how many of those numbers start with the digit 6.

Q2:

How many three-digit numbers, which have an even tens digit and no repeated digits, can be formed using the elements of the set { 5 , 8 , 9 , 2 } ?

Q3:

How many four-digit numbers, with no repeated digits, can be formed using the elements of the set { 0 , 1 , 3 , 4 } ?

Q4:

After a recent reorganisation, Nabil is taking over responsibility for the manufacturing of odd numbers on the house sign number production line. As part of his scientific investigation into production levels, he wants to know how many three digit numbers only contain odd digits. Calculate the answer for him.

Q5:

In how many ways can a 9-digit code be formed using the numbers 1 to 9? Note, the code can have repeated digits.

Q6:

How many three-digit even numbers, with no repeated digits, can be formed using the elements of the sets { 3 , 8 , 9 , 2 } ?

Q7:

Find the number of ways to form a 2-digit number, with no repeated digits, given 4 diﬀerent digits to choice from.

Q8:

Phone numbers on a particular network are twelve-digit long, where the first three digits are always 072. Calculate the total number of different phone numbers which the network can use.

Q9:

In how many ways can an odd number of 6 digits be formed using the numbers 1 , 2 , 3 , 4 , 5 , 6 if no digits are to be repeated?

Q10:

How many two-digit numbers, which end with the digit 2 and have no repeated digits, can be formed using the elements of the set { 3 , 1 , 2 } ?

Q11:

Determine the number of ways a 7-digit number can be formed from 7 different digits, excluding zeros, given that each digit can NOT be used more than once.

Q12:

How many three-digit numbers, which are less than 900 and have no repeated digits, can be formed using the elements of the set { 7 , 1 , 9 } ?

Q13:

In how many ways can a three-digit number, starting with an even digit and containing no repeated digits, be formed from the numbers 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ?

Q14:

How many three-digit numbers can be formed by picking the units digit from the set { 8 } , the tens digit from the set { 8 , 6 , 1 , 2 } , and the hundreds digit from the set { 2 , 6 , 1 } ?

Q15:

Without repeating any of the digits, determine how many numbers can be formed from the digits of the number 54 321, and find out how many of those numbers start with the digit 4 and end with the digit 1.

Q16:

A building has 5 doors which are numbered as 1 , 2 , 3 , 4 , 5 . Determine the number of ways a person can enter, and then leave the building, if they cannot use the same door twice.

Q17:

In a gallery, each painting is referenced by three distinct English letters, and a four-digit number which has no zeros and no repeated digits. How many paintings can be referenced using this system?

Q18:

In how many ways can a 3-digit number, which is greater than 300 and has no repeated digits, be formed using the numbers 1 , 2 , 3 , 4 , 5 , 6 ?

Q19:

In how many ways can a 4-digit even number, with no repeated digits, be formed using the elements of the set { 1 , 6 , 9 , 8 , 7 , 5 } ?

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