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  • Question
  • An intelligence agency forms a code of two distinct digits selected from 0, 1, 2,....., 9 such that the first-digit of code is non-zero. The code, handwritten on a slip, can however potentially create confusion when read upside down, for examples the code 91 may appear as 16. how many codes are there for which no such confusion can arise?


  • Options
  • A. 80
  • B. 78
  • C. 71
  • D. 69

  • Correct Answer
  • 69 

    Explanation

    The available digits are 0, 1, 2,...., 9. The first digit can be chosen in 9 ways (0 not acceptable), the second digit can be accepted in 9 ways (digit repetition not allowed). Thus, the code can be made in 9 x 9 = 81 ways.
    Now, there are only 4 digits which can create confusion 1, 6, 8, 9. The same can be given in the following ways
    Total number of ways confusion can arise
    = 4 x 3 = 12
    Thus, the ways in which no such confusion arise = 81-12 =69


  • Permutation and Combination problems


    Search Results


    • 1. 
      A new flag is to be designed with six vertical stripes using some or all of the colour yellow, green,blue and red. Then, the number of ways this can be made such that no two adjacent stripes have the same colour is

    • Options
    • A. 12 x 81
    • B. 16 x 192
    • C. 20 x 125
    • D. 24 x 216
    • Discuss
    • 2. 
      A five-digit number divisible by 3 is to be formed using digits 0, 1, 2, 3, 4 and 5 without repetition, the total number of ways this can be done, is

    • Options
    • A. 122
    • B. 210
    • C. 216
    • D. 217
    • Discuss
    • 3. 
      The number of ways in which a committee of 3 ladies and 4 gentlemen can be appointed from a group consisting of 8 ladies and 7 gentlemen, if Mrs. X refuses to serve in a committee if Mr. Y is its member, is

    • Options
    • A. 1960
    • B. 3240
    • C. 1540
    • D. None of these
    • Discuss
    • 4. 
      There are 10 stations on a railway line. The number of different journey tickets that are required by the authorities, is

    • Options
    • A. 92
    • B. 90
    • C. 91
    • D. 93
    • Discuss
    • 5. 
      A question paper consists of two sections having respectively 3 and 5 questions. The following note is given on the paper. "It is not necessary to attempt all the question". One question from each section is compulsory. In how many ways, a candidate can select the question?

    • Options
    • A. 38
    • B. 217
    • C. 256
    • D. 320
    • Discuss
    • 6. 
      How many numbers can be formed from 1, 2, 3, 4, 5, ( without repetition), when the digit at the unit's place must be greater than that in the ten's place?

    • Options
    • A. 54
    • B. 60
    • C. 51/3
    • D. 2 x 4!
    • Discuss
    • 7. 
      Boxes numbered 1, 2, 3, 4, and 5 are kept in a row and they are to be filled with either a red or a blue ball, such that no two adjacent boxes can be filled with blue balls. Then, how many different arrangements are possible, given that all balls of a given colour are exactly identical in all respects?

    • Options
    • A. 8
    • B. 10
    • C. 15
    • D. 22
    • Discuss
    • 8. 
      Marks obtained by an student in 5 subjects are given below 25, 26, 27, 28, 29 in these obtained marks 27 is

    • Options
    • A. mode
    • B. median and mode
    • C. mean and median
    • D. both (a) and (c)
    • Discuss
    • 9. 
      The median for the data 2, 4, 6, 8, 10, 12, 14 is

    • Options
    • A. 6
    • B. 8
    • C. 9.5
    • D. 10
    • Discuss
    • 10. 
      Reaching the place of meeting on Tuesday 15 min before 8:30 h, Anuj found himself half an hour earlier than the man who was 40 min late. What was the scheduled time of the meeting?

    • Options
    • A. 8:00 h
    • B. 8:05 h
    • C. 8:15 h
    • D. 8:45 h
    • Discuss


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