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  • Question
  • Which of the following is not a prime number?


  • Options
  • A. 5
  • B. 11
  • C. 21
  • D. 37

  • Correct Answer
  • 21 

    Explanation

    A prime number is a whole number greater than 1 whose only factors are 1 and itself.

     

    Factors of 5 are 1, 5

    Factors of 11 are 1, 11

    Factors of 21 are 1, 3, 7, 21

    Factors of 37 are 1, 37.

     

    Hence, according to the definition of a prime number, 21 is not a prime number as it has more than two factors.


  • Numbers problems


    Search Results


    • 1. A sequence of natural number 2,3,5,6,10. Such that no square and no cube occurs in the term. Find the 300th term of sequence ?

    • Options
    • A. 322
    • B. 319
    • C. 321
    • D. 320
    • Discuss
    • 2. How many digits will be there to the right of the decimal point in the product of 95.75 and 0.2554 ?

    • Options
    • A. 6
    • B. 7
    • C. 8
    • D. 9
    • Discuss
    • 3. A box contains 90 screws each of 100 gms and 100 bolts each of 150 gms. If the entire box weighs 35.5 kg, then the weight of the empty box is ?

    • Options
    • A. 10.5 kgs
    • B. 12 kgs
    • C. 9.6 kgs
    • D. 11.5 kgs
    • Discuss
    • 4. What is the right most integer of the expression 65776759 + 54697467 ?

    • Options
    • A. 4
    • B. 6
    • C. 9
    • D. 0
    • Discuss
    • 5. A teacher multiplies 987 by a certain number and obtains 556781 as her answer. If in the answer, both 6 and 7 are wrong but the other digits are correct, then the correct answer will be

    • Options
    • A. 553681
    • B. 555181
    • C. 556581
    • D. 555681
    • Discuss
    • 6. What should be the maximum value of B in the following equation? 8A9 ? 6B2 + 4C6 = 723

    • Options
    • A. 4
    • B. 1
    • C. 5
    • D. 7
    • Discuss
    • 7. How many prime numbers exist in 65×359×113 ?

    • Options
    • A. 29
    • B. 31
    • C. 33
    • D. 27
    • Discuss
    • 8. There are several peacocks and deers in a cage (with no other types of animals). There are 72 heads and 200 feet inside the cage. How many peacocks are there, and how many deers ?

    • Options
    • A. 42 & 24
    • B. 38 & 26
    • C. 36 & 24
    • D. 44 & 28
    • Discuss
    • 9. In a colored picture of blue and yellow color, blue and yellow color is used in the ratio of 4:3 respectively. If in upper half, blue : yellow is 2:3, then in the lower half blue : yellow is

    • Options
    • A. 1 : 1
    • B. 2 : 1
    • C. 26 : 9
    • D. 9 : 26
    • Discuss
    • 10. What is the measure of an interior angle of a regular decagon?

    • Options
    • A. 120°
    • B. 140°
    • C. 144°
    • D. 150°
    • Discuss


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