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ICSE-VIII-Mathematics

05: Playing with Number Class 8 Maths

with Solutions - page 3

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  • Qstn #10
    Answer
    5 + A = 13
    And A + 4 = 13
    ∴ A = 13 - 5 = 8
    Hence A = 8
  • Qstn #11
    Answer
    C + 5 = 11
    ∴ C = 11 - 5 = 6
    And 8 + B + 1 = 15
    ∴ B = 15 - 9 = 6
    And A + 5 + 1 = 13
    ∴ A = 13 - 6 = 7
    And 6 + D + 1 = 9
    ∴ D = 9 - 7 = 2
    Hence A = 7, B = 6, C = 6 and D = 2
  • #
    Section : C
  • Qstn #1
    Find which of the following numbers are divisible by 2: (i) 192 (ii) 1660 (iii) 1101 (iv) 2079
    Ans : A number having its unit digit 2, 4, 6, 8 or 0 is divisible by 2.
    So, Number 192, 1660 are divisible by 2.
  • Qstn #2
    Find which of the following numbers are divisible by 3: (i) 261 (ii) 111 (iii) 6657 (iv) 2574
    Ans : A number is divisible by 3 if the sum of its digits is divisible by 3,
    So, 261, 111 are divisible by 3.
  • Qstn #3
    Find which of the following numbers are divisible by 4: (i) 360 (ii) 3180 (iii) 5348 (iv) 7756
    Ans : A number is divisible by 4, if the number formed by the last two digits is divisible by 4.
    So, number 360, 5348, 7756 are divisible by 4.
  • Qstn #4
    Find which of the following numbers are divisible by 5 : (i) 3250 (ii) 5557 (iii) 39255 (iv) 8204
    Ans : A number having its unit digit 5 or 0, is divisible by 5.
    So, 3250, 39255 are all divisible by 5.
  • Qstn #5
    Find which of the following numbers are divisible by 4: (i) 360 (ii) 3180 (iii) 5348 (iv) 7756
    Ans : A number having its unit digit 0, is divisible by 10.
    So, 5100, 3400 are all divisible by 10.
  • Qstn #6
    Which of the following numbers are divisible by 11: (i) 2563 (ii) 8307 (iii) 95635
    Ans : A number is divisible by 11 if the difference of the sum of digits at the odd places and sum of the digits at even places is zero or divisible by 11.
    So, 2563 is divisible by 11.
  • #
    Section : D
  • Qstn #1
    For what value of digit x, is :
  • #1-1
    × 5 divisible by 3?
    Ans : × 5 is divisible by 3
    ⇒ 1 + x + 5 is a multiple of 3
    ⇒ 6 + x = 0, 3, 6, 9
    Since, x is a digit
    x = 0, 3, 6 or 9
  • Qstn #2
    31 × 5 is divisible by 3?
    Ans : 31 × 5 is divisible by 3
    ⇒ 3 + 1 + x + 5 is a multiple of 3
    ⇒ 9 + x = 0, 3, 6, 9,
    ⇒ x = -9 , -6, -3, 0, 3, 6, 9,
    Since, x is a digit
    x = 0, 3, 6 or 9
  • Qstn #3
    28 × 6 is a multiple of 3?
    Ans : 28 × 6 is a multiple of 3
    2 + 8 + x + 6 is a multiple of 3
    ⇒ 16 + x = 0, 3, 6, 9, 12, 15,18
    ⇒ x = -18, -5, -2, 0, 2, 5, 8
    Since, x is a digit = 2, 5, 8
  • Qstn #4
    24x divisible by 6?
    Ans : 24x is divisible by 6
    ⇒ 2 + 4 + x is a multiple of 6
    ⇒ 6 + x = 0, 6, 12
    ⇒ x = -6, 0, 6
    Since, x is a digit
    x = 0, 6
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