Permutation and Combination
Fundamental Principle of Counting
“If an event can occur in m different ways, following which another eventcan occur in n different ways, then the total number of occurrence of the eventsin the given order is m×n.”
Q1.Ten horses are running in a race. In how many ways can these horses come in the first, second, third place, assuming no ties?
Q2.There are five bus services running between Delhi and Mumbai. In how many wayscan a man go from Delhi to Mumbai and return by a different service?
Q3.John wants to go abroad by ship and return by air. He has a choice of six different ships to go and four airlines to return. In how many ways can he perform his journey?
Q4.There are 6 multiple choice questions on an examination. How many sequences of answers are possible, if the first three questions have 4 choices each and the next three have 5 each?
Q5a) There are 5 true – false questions on an examination. How many sequences of answers are possible?
b) If no student has written all correct answers and no two students have given the same sequence of answers. What is the maximum number of students in the class, for this to be possible?
Q6 a) How many numbers are there between 100 & 1000 such that 7 is in the unit’s place?
b)How many numbers are there between 100 & 1000 such that at least one of their digits is 7?
Q7 A mint prepares metallic calendars specifying months, dates and days in the form of monthly sheets (one plate for each month). How many types of February calendars should it prepare to serve for all the possibilities in the future years?
Q8. A coin is tossed three times and the outcomes are recorded. How many possible outcomes are there? How many possible outcomes are there if the coin is tossed four times?
Q9. Four tourists have a choice of 5 hotels in a city. Each wants to stay in a different hotel. Find the number of ways in which they can make thechoice.
Q10. Five persons entered the lift cabin on the ground of an 8-floor house. Suppose each of them can leave the cabin independently at any floor beginning with the first. Find the total number of ways in which each of the five persons can leave the cabin
(i)at any one of the 7 floors
(ii)at different floors.
Q11.How many words with or without meaning of three distinct letters of the English alphabets are there ?
Q12. Find the total number of ways answering 5 objective type questions, each question having 4 choices.
Factorial Notation:
The notation n! represents the product of first n natural numbers
Q1.Evaluate:
Q2. Find the L.C.M of the number 4!,5! & 6!
Q3. If (n +2 )! =60 [(n-1)!], find n.
Q4. If and are in the ratio 2:1, find the value of n.
Q5. Prove that
= 1.3.5…… (2n-1)
Permutation
Definition 1A permutation is an arrangement in a definite order of a number ofobjects taken some or all at a time.
Theorem 1The number of permutations of n different objects taken r ata time,where 0 < r ≤n and the objects do not repeat is
n ( n – 1) ( n – 2). . .( n – r + 1),which is denoted by nPr.
Theorem 2The number of permutations of n different objects taken r at a time,where repetition is allowed, is nr.
Theorem 3The number of permutations of n objects, where p objects are of thesame kind and rest are all different is
Theorem 4The number of permutations of n objects, where p1 objects are of onekind, p2 are of second kind, ..., pkare of kth kind and the rest, if any, are of differentkind is
Permutation
Q1. There are 3 different rings to be worn in four fingers with at most one in each finger. In how many ways can this be done?
Q2. There are 6 items in columns A and 6 items in column B. A student is asked to match each item in column A with an item in column B. How many possible answers (correct or incorrect) are there to the question?
Q3. How many 3-letter words can be made using the letters of the word ORIENTAL?
Q4.The letters of the word WEDNESDAY are arranged in a line, each arrangement endingwith letter S. How many different arrangements are possible? How many of them start with letter D?
Q5.In how many ways can 6 boys and 5 girls be arranged for a group photograph if the girls are to sit on chairs in a row and the boys are to stand in a row behind them?
Q6. The letters of the word PROMISE are arranged so that no two of the vowels should come together. Find the total number of arrangements.
Q7. A family of 4 brothers and 3 sisters is to be arranged for a photograph in one row. In how many ways can they be seated if
(i)all the sisters sit together
(ii)No 2 sisters sit together
Q8. In how many ways can the letter of the word DELHI be arranged so that the letters E and I occupy only even places?
Q9. In how many ways can the letters of the word ‘FRACTION’ be arranged so that no two vowels are together?
Q10. In how many ways can 6 plastic beads of different colours be arranged so that the blue and green beads are never placed together?
Q11.7 candidates are to take examination, 2 in mathematics and remaining in different subjects. In how many ways can they be seated in a row so that the two examinees in Mathematics may not sit together?
Q12. In how many ways can the letters of the word ‘STRANGE’ be arranged so that the vowels may appear in the odd places?
Q13. In how many ways can the letters of the word ‘MODESTY’ be arranged so that
(i)D and E are always together
(ii)D and E are never together.
Q14. How many numbers greater than 4000 can be formed using the digits 2,3,4,5,6 when no digit is repeated?
Q15.How many numbers of six digits can be formed from the digits 1,2,3,4,5,6 (no digit being repeated)? How many of these are not divisible by 5?
Q16.How many of the natural numbers from 1 to 1000 have none as their digits repeated?
Q17. How many numbers lying between 100 & 1000 can be formed using the digits 2,3,0,8,9 (no digit being repeated).
Q18.How many different 4-digit numbers can be formed from the digits 2, 3,4and 6 if each digit is used only once in a number? Further, how many of these numbers
(i)end in a 4?
(ii)end in a 3?
(iii)end in a 3 or 6?
Q19. How many arrangements are possible for the 9 books to be arranged on a shelf so that
(i) 3 of the books are always together.
(ii)3 of the books are never together.
Q20. How many 3 digit odd numbers are possible by using 1,2,3,4,5,6 when repetition of digits is allowed.
Q21. In an examination hall there are four rows of chairs. Each row has 8 chairs one behind the other. There are two classes sitting for the examination with 16 students in each class. It is desired that in each row, all students belong to same classand that no two adjacent rows are allotted to the same class . In how many ways can these 32 students be seated?
Q22. Find the sum of all the numbers that can be formed with the digits 2,3,4,5 taken all at a time.
Q23. When a group photograph is taken, all the seven teachers should be in the first row and all the twenty students should be in the second row. If the two corners are reserved for two tallest students,interchangeable only between them and, if the middle seat of the front row is reseved for the Principal. How many arrangements are possible?
Q24. How many even numbers are there with three digits such that if 5 is one of one of the digits , then 7 is the next digit?
Q25. The Principal wants to arrange 5 students on the platform such that the boy ‘SALIM’ accepts the second position and such that the girl, ‘SITA’ is always adjacent to the girl ‘RITA’ . How many such arrangements are possible?
Q26. A tea party is arranged for 16 persons along two sides of a table with 8 chairs on each side.Four persons wish to sit on one paticular and two on the other side . In how many ways can they be seated?
Q27. The letters of the word ‘RANDOM’ are written in all possible orders and these words are written out as in a dictionary. Find the rank of the word ‘RANDOM’.
Q28. There are six periods in each working day of a school, in how many ways can one arrange 5 subjects such that each subjectis allowed at least one period?
Permutations with repetitions
Q1.There are 4 candidates for the post of a lecturer in Mathematics and one is to be selected by votes of 5 men. In how many ways can the votes be given?
Q2. In how many ways can 6 rings be worn on the four fingers of one hand?
Q3. There are 3 prizes to be distributed among 5 students. In how many ways can it be done when
(i)No student gets more than one prize
(ii)There is no restrictions to the number of prizes any student gets
(iii)No student gets all the prizes.
Permutations when all the objects are not distinct
Q1. In how many different ways can the letters of the word “KURUKSHETRA” be arranged?
Q2. There are 3 blue balls, 4 red balls and 5 green balls. In how many ways can they be arranged in a row?
Q3. In how many arrangements of the letters of the word ‘MATHEMATICS ‘ the vowels occur together?
Q4. How many words can be formed using the letter A thrice, the letter B twice and the letter C once?
Q5. In how many ways can 10- paise coin, two 20 paise, three 25 paise and one 50 paise coins be distributed among 8 children so that each child gets only one coin?
Q7. In how many ways distinct ways can the product xy2z2 be written without using exponents?
Q8. How many different permutations from the letters of the word ‘ALABAMA’ contain the word LAMB?
Q 9. In how many ways can the letters of the word BALLOON be arranged so that two L’s do not come together?
Q10. How many numbers can be formed with the digits 1,2,3,4,3,2,1 so that the odd digits always the odd places?
Combination
The number of combinations of n different things taken r at a time, denoted bynCr, is given by
Theorem 5
Q1 .Evaluate: C (13,6 ) + C(13,5)
Q2. Verify the equality 2 C (7,4 ) = C (8,4)
Q3. Find the value of r if C(n, r-1) = 36, C(n, r) = 84 & C(n, r+1) = 126,then find C(r,2)
Q4. Find the value of n if nPr = 840, nCr =35,
Q5. Find the value of n and r if n Cr =56 and n Pr = 336
Q6. Find the values of n and r if nPr = n P r+1 and nC r = nCr-1.
Q7. Prove that
2n C n =2 n. n! [ 1 .3 .5…….(2n-1) ]
n!
Q8. Prove that nCr * rCs = nCs * n-sCr-s
Q9. Prove that nCr+2. nCr-1 +nCr-2 = n+2Cr
Word Problems
Q1. In how many ways can a cricket eleven has to be chosen out of a batch of 15 players if
i)There is no restriction on the selection;
ii)A particular player is always chosen;
iii)A particular player is never chosen ?
Q2. Every body in a room shakes hands with everybody else. If the total number of handshakes is66, then find the total number of persons in the room?
Q3.Find the total number of ways in which 5 red and 4 white balls can be drawn out of 10 red and 9 white balls?
Q4.In how many ways a committee of 5 members can be selected from 6 men and 5 ladies consisting of 3 men and 2 ladies?
Q5.Determine the number of 5 cards combinations out of a deck of 52 cards if there is atleast one ace in each combination.
Q6. An examination paper consists of 12 questions divided in to parts A and B .Part A contains 7 questions and part B contains 5 questions. A candidate is required to attempt 8 questions selecting at least 3 from each part. In how many ways can the candidate select the questions?
Q7. From a class of 12 boys and 10 girls, 10 students are to be chosen for a competition, at least including 4 boys and 4 girls. The 2 girls who won the prizes last year should be included. In how many ways can the selection be made?
Q8. Determine the number of 3 cards combinations out of a deck of 52 cards if at least one of 3 cards is to be spade?
Q9. A boy has 3 library tickets and 8 books of its interest in the library. Of these 8, he does not want to borrow chem. Part II unless chem. PartI is also borrowed. In how many ways can he choose the three books to be borrowed?
Q10. A polygon has 44 diagonals. Find the number of its sides?
Q11. How many diagonals can be drawn by joining the vertices of an octagon?
Q12. There are 10 points in a plane, no three of which are in the same straight line excepting 4, which are collinear. Find the number of
(i)straight lines
(ii)triangle formed by joining them.
Q13. Find the total number of ways of selecting five letters of the word INDEPENDENT.
Q14. A man has 7 relatives , 4 of them are ladies and 3 gentlemen , his wife has 7 relatives and 3 of them are ladies and 4 gentlemen . In how many ways can they invite a dinner party of 3 ladies & 3 gentlemen so that there are 3 of man’s relatives and 3 of wife’s relatives?
Q15. Find the total number of ways if six '+' and four '- ' are to be placed in a straight line so that no two '- 'signs come together?