This section covers permutations and combinations.

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Arvarying Objects

The variety of means of arranging n unfavor objects in a line is n! (pronounced ‘n factorial’). n! = n × (n – 1) × (n – 2) ×…× 3 × 2 × 1


How many various means deserve to the letters P, Q, R, S be arranged?

The answer is 4! = 24.

This is because there are four spaces to be filled: _, _, _, _

The initially area deserve to be filled by any type of one of the four letters. The second room have the right to be filled by any type of of the remaining 3 letters. The 3rd space can be filled by any kind of of the 2 staying letters and also the final space should be filled by the one staying letter. The full number of possible arrangements is therefore 4 × 3 × 2 × 1 = 4!

The number of ways of arranging n objects, of which p of one kind are achoose, q of a second type are aprefer, r of a 3rd form are aprefer, etc is:

n! .p! q! r! …


In exactly how many type of methods have the right to the letters in the word: STATISTICS be arranged?

Tright here are 3 S’s, 2 I’s and also 3 T’s in this word, therefore, the variety of methods of arranging the letters are:

10!=50 4003! 2! 3!

Rings and Roundabouts

The variety of ways of arvarying n unlike objects in a ring when clockwise and anticlockwise arrangements are various is (n – 1)!

When clockwise and also anti-clockwise arrangements are the very same, the number of ways is ½ (n – 1)!


Ten world go to a party. How many type of different means can they be seated?

Anti-clockwise and also clockwise arrangements are the very same. Therefore, the total number of ways is ½ (10-1)! = 181 440


The number of ways of choosing r objects from n unprefer objects is:



Tbelow are 10 balls in a bag numbered from 1 to 10. Three balls are selected at random. How many kind of various means are tright here of selecting the 3 balls?

10C3 =10!=10 × 9 × 8= 120 3! (10 – 3)!3 × 2 × 1


A permutation is an ordered arrangement.

The variety of ordered arrangements of r objects taken from n unchoose objects is:

nPr = n! . (n – r)!


In the Match of the Day’s goal of the month competition, you had to pick the height 3 goals out of 10. Because the order is necessary, it is the permutation formula which we use.

10P3 =10! 7!

= 720

There are therefore 720 various ways of picking the top three purposes.


The above facts have the right to be provided to assist settle troubles in probcapacity.


In the National Lottery, 6 numbers are preferred from 49. You win if the 6 balls you pick match the 6 balls selected by the machine. What is the probability of winning the National Lottery?

The variety of ways of selecting 6 numbers from 49 is 49C6 = 13 983 816 .

See more: How Many Milliliters Are Contained In 1M3 ? Cubic Meters To Milliliters

As such the probcapacity of winning the lottery is 1/13983816 = 0.000 000 071 5 (3sf), which is about a 1 in 14 million possibility.