Number System: Aptitude Questions and Answers-6


Overview:


Questions and Answers Type:MCQ (Multiple Choice Questions).
Main Topic:Quantitative Aptitude.
Quantitative Aptitude Sub-topic:Number System Aptitude Questions and Answers.
Number of Questions:10 Questions with Solutions.

  1. Find the smallest positive number which is exactly divisible by 3, 6, and 10?

    1. 20
    2. 30
    3. 40
    4. 50


Answer: (b) 30

Solution:

Step(1): Factorize the numbers into their prime factors.$$ 3 = 3^{1} $$ $$ 6 = 2^{1} \times 3^{1} $$ $$ 10 = 2^{1} \times 5^{1} $$ Step(2): Collect all the distinct factors with their maximum available power.$$ = 2^{1}, \ 3^{1}, \ 5^{1} $$ Step(3): Multiply the collected factors.$$ = 2 \times 3 \times 5 = 30 $$ Here, 30 is the smallest positive number which is exactly divisible by 3, 6, and 10.


  1. Find the LCM of 15, 20, 27?

    1. 460
    2. 480
    3. 540
    4. 560


Answer: (c) 540

Solution:

Step(1): Factorize the numbers into their prime factors.$$ 15 = 3 \times 5 = 3^{1} \times 5^{1} $$ $$ 20 = 2 \times 2 \times 5 = 2^{2} \times 5^{1} $$ $$ 27 = 3 \times 3 \times 3 = 3^{3} $$ Step(2): Collect all the distinct factors with their maximum available power.$$ = 2^{2}, \ 3^{3}, \ 5^{1} $$ Step(3): Multiply the collected factors.$$ = 2^{2} \times 3^{3} \times 5^{1} $$ $$ = 4 \times 27 \times 5 = 540 $$ Here, 540 is the smallest positive number which is exactly divisible by 15, 20, and 27.


  1. Find the LCM of \(\frac{8}{7}\) and \(\frac{9}{5}\)?

    1. 36
    2. 49
    3. 65
    4. 72


Answer: (d) 72

Solution: \(LCM \ of \ fractions = \frac{LCM \ of \ Numerators}{HCF \ of \ Denominators}\) $$ LCM = \frac{LCM \ of \ (8,9)}{HCF \ of \ (7,5)} $$ $$ = \frac{72}{1} = 72 $$

  1. Find the LCM of \(\frac{10}{7}\), \(\frac{15}{4}\), and \(\frac{18}{11}\)?

    1. 60
    2. 80
    3. 90
    4. 120


Answer: (c) 90

Solution: \(LCM \ of \ fractions = \frac{LCM \ of \ Numerators}{HCF \ of \ Denominators}\) $$ LCM = \frac{LCM \ of \ (10, 15, 18)}{HCF \ of \ (7, 4, 11)} $$ $$ = \frac{90}{1} = 90 $$

  1. Which of the following is the LCM of 25, \(\frac{15}{7}\), and 20?

    1. 150
    2. 180
    3. 280
    4. 300


Answer: (d) 300

Solution: \(LCM \ of \ fractions = \frac{LCM \ of \ Numerators}{HCF \ of \ Denominators}\) $$ LCM = \frac{LCM \ of \ (25, 15, 20)}{HCF \ of \ (1, 7, 1)} $$ $$ = \frac{300}{1} = 300 $$

  1. 150 is the LCM of, which of the following numbers of a group?

    1. 25, 15, 10, 5
    2. 20, 15, 10, 5
    3. 25, 20, 15, 10
    4. 15, 12, 10, 5


Answer: (a) 25, 15, 10, 5

Solution: 150 is the LCM of 25, 15, 10, 5.

  1. Find the LCM of 56, 78, 99?

    1. 72056
    2. 72072
    3. 76210
    4. 78520


Answer: (b) 72072

Solution:

Step(1): Factorize the numbers into their prime factors.$$ 56 = 2 \times 2 \times 2 \times 7 = 2^{3} \times 7^{1} $$ $$ 78 = 2 \times 3 \times 13 = 2^{1} \times 3^{1} \times 13^{1} $$ $$ 99 = 3 \times 3 \times 11 = 3^{2} \times 11^{1} $$ Step(2): Collect all the distinct factors with their maximum available power.$$ = 2^{3}, \ 3^{2}, \ 7^{1} \ 11^{1} \ 13^{1} $$ Step(3): Multiply the collected factors.$$ = 2^{3} \times 3^{2} \times 7^{1} \times 11^{1} \times 13^{1} $$ $$ = 8 \times 9 \times 7 \times 11 \times 13 = 72072 $$


  1. 180 is the LCM of, which of the following numbers of a group?

    1. 5, 12, 16, 45
    2. 9, 15, 18, 60
    3. 15, 18, 25, 50
    4. 10, 15, 20, 25


Answer: (b) 9, 15, 18, 60

Solution: 180 is the LCM of 9, 15, 18, 60.

  1. Which of the following is the LCM of \(\frac{10}{9}\), 9, and \(\frac{3}{10}\)?

    1. 60
    2. 90
    3. 100
    4. 120


Answer: (b) 90

Solution: \(LCM \ of \ fractions = \frac{LCM \ of \ Numerators}{HCF \ of \ Denominators}\) $$ LCM = \frac{LCM \ of \ (10, 9, 3)}{HCF \ of \ (9, 1, 10)} $$ $$ = \frac{90}{1} = 90 $$

  1. Find the LCM of 35, 40, and 50?

    1. 900
    2. 1200
    3. 1400
    4. 1500


Answer: (c) 1400

Solution:

Step(1): Factorize the numbers into their prime factors.$$ 35 = 5^{1} \times 7^{1} $$ $$ 40 = 2 \times 2 \times 2 \times 5 = 2^{3} \times 5^{1} $$ $$ 50 = 2 \times 5 \times 5 = 2^{1} \times 5^{2} $$ Step(2): Collect all the distinct factors with their maximum available power.$$ = 2^{3}, \ 5^{2}, \ 7^{1} $$ Step(3): Multiply the collected factors.$$ = 2^{3} \times 5^{2} \times 7^{1} $$ $$ = 8 \times 25 \times 7 = 1400 $$