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Numbers Questions Answers

  • 1. Simplify 586645 * 9999

    1. 5865863355
    2. 5665863355
    3. 4865863355
    4. 4665863355
    Answer And Explanation

    Answer: Option A

    Explanation:

    Although it is a simple question, but the trick is to save time in solving this.
    Rather than multiplying it we can do as follows:
    586645 * (10000 - 1) = 5866450000 - 586645 = 5865863355

  • 2. 1939392 * 625

    1. 1212120010
    2. 1212120000
    3. 1212120011
    4. 1212121010
    Answer And Explanation

    Answer: Option B

    Explanation:

    Trick: when multiplying with \begin{aligned} 5^n
    \end{aligned} then put n zeros to the right of multiplicand and divide the number with \begin{aligned} 2^n
    \end{aligned}
    So using this we can solve this question in much less
    time.
    \begin{aligned} 1939392 \times 5^4 = \frac {19393920000}{16} = 1212120000
    \end{aligned}

  • 3. Simplify (212 * 212 + 312 * 312 )

    1. 132288
    2. 142088
    3. 142188
    4. 142288
    Answer And Explanation

    Answer: Option D

    Explanation:

    Trick: Above equation can be solved by using following formula
    \begin{aligned}
    (a^2 + b^2) = \frac{1}{2}((a+b)^2 + (a-b)^2)
    \end{aligned}

  • 4. Find the unit digit in \begin{aligned}
    (544)^{102} + (544)^{103}
    \end{aligned}

    1. 2
    2. 4
    3. 0
    4. 1
    Answer And Explanation

    Answer: Option C

    Explanation:

    Required digit is = \begin{aligned}
    (4)^{102} + (4)^{103} \end{aligned}
    as \begin{aligned} (4)^2 \end{aligned} gives unit digit 6 so \begin{aligned} (4)^{102} \end{aligned} unit digit is 6 and \begin{aligned} (4)^{103} \end{aligned} unit digit is, unit digit of \begin{aligned} 6 \times 4 \end{aligned}= 4, so answer will be unit digit of 6 + 4 = 0

  • 5. What least value should be replaced by * in 223*431 so the number become divisible by 9

    1. 3
    2. 4
    3. 5
    4. 6
    Answer And Explanation

    Answer: Option A

    Explanation:

    Trick: Number is divisible by 9, if sum of all digits is divisible by 9, so (2+2+3+*+4+3+1) = 15+* should be divisible by 9,
    15+3 will be divisible by 9,
    so that least number is 3.

  • 6. How many terms are there in 2,4,8,16,....,1024

    1. 7
    2. 8
    3. 9
    4. 10
    Answer And Explanation

    Answer: Option D

    Explanation:

    It is a GP. with r = 2, ie \begin{aligned} 2^1, 2^2, 2^3... \end{aligned}
    If number of terms is n. Then,
    \begin{aligned} 2 \times 2^{n-1} = 1024 \end{aligned} =>
    \begin{aligned} 2^{n-1} = 512 \end{aligned}
    or \begin{aligned} 2 \times 2^{n-1} = 2^9 \end{aligned}
    so n-1 = 9 => n = 10

  • 7. Which of the following is a prime number

    1. 9
    2. 2
    3. 4
    4. 8
    Answer And Explanation

    Answer: Option B

    Explanation:

    A prime number is a natural number greater than 1 which has no positive divisors other than 1 or itself.
    So from above options 2 is that number