Simplification


  1. If the sum of squares of two real numbers is 41 and their sum is 9, then the sum of cubes of these two numbers is









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    Let the two real numbers be x and y.
    According to the question,
    x2 + y2 = 41
    x + y = 9
    ∴  (x + y)2 = x2 + y2 + 2xy
    ⇒  81 = 41 + 2xy
    ⇒  2xy = 81 – 41 = 40

    ⇒  xy =
    40
    = 20
    2

    ∴  x3 + y3 = (x + y)3 – 3xy (x + y)
    = (9)3 – 3 × 20 (9)
    = 729 – 540 = 189

    Correct Option: C

    Let the two real numbers be x and y.
    According to the question,
    x2 + y2 = 41
    x + y = 9
    ∴  (x + y)2 = x2 + y2 + 2xy
    ⇒  81 = 41 + 2xy
    ⇒  2xy = 81 – 41 = 40

    ⇒  xy =
    40
    = 20
    2

    ∴  x3 + y3 = (x + y)3 – 3xy (x + y)
    = (9)3 – 3 × 20 (9)
    = 729 – 540 = 189


  1. Find the least number which must be subtracted from 18265 to make it a perfect square.









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    ∴  Required answer = 40

    Correct Option: C


    ∴  Required answer = 40



  1. If a perfect square, not divisible by 6, be divided by 6, the remainder will be









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    Remainder on dividing 32 = 9 by 6 = 3
    Remainder on dividing 42 = 16 by 6 = 4
    Remainder on dividing 52 = 25 by 6 = 1

    Correct Option: C

    Remainder on dividing 32 = 9 by 6 = 3
    Remainder on dividing 42 = 16 by 6 = 4
    Remainder on dividing 52 = 25 by 6 = 1


  1. The greatest perfect square number of 6 digits is









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    Largest 6-digit number = 999999

    ∴  Required perfect square number = 999999 – 1998 = 998001

    Correct Option: B

    Largest 6-digit number = 999999

    ∴  Required perfect square number = 999999 – 1998 = 998001



  1. three numbers are such that their sum is 50, product is 3750 and the sum of their reciprocals is 31/50 .Find the sum of the squares of the three numbers.









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    x + y + z = 50 ; xyz = 3750

    ∴ 
    1
    +
    1
    +
    1
    =
    yz + zx + xy
    xyzxyz

    =
    31
    150

    ⇒  xy + yz + zx =
    31
    xyz
    150

    =
    31
    × 3750 = 775
    150

    ∴  (x + y + z )2 = x2 + y2 + z2 + 2(xy + yz + zx)
    ⇒  (50)2 + x2 + y2 + z2 + 2 × 775
    ⇒  2500 = x2 + y2 + z2 + 1550
    ⇒  x2 + y2 + z2 = 2500 – 1550
    = 950

    Correct Option: C

    x + y + z = 50 ; xyz = 3750

    ∴ 
    1
    +
    1
    +
    1
    =
    yz + zx + xy
    xyzxyz

    =
    31
    150

    ⇒  xy + yz + zx =
    31
    xyz
    150

    =
    31
    × 3750 = 775
    150

    ∴  (x + y + z )2 = x2 + y2 + z2 + 2(xy + yz + zx)
    ⇒  (50)2 + x2 + y2 + z2 + 2 × 775
    ⇒  2500 = x2 + y2 + z2 + 1550
    ⇒  x2 + y2 + z2 = 2500 – 1550
    = 950