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Nick's Mathematical Puzzles: 91 to 100

91. Nonagon diagonals (2 star)

In regular nonagon ABCDEFGHI, show that AF = AB + AC.

Regular nonagon ABCDEFGHI, showing diagonals AC and AF.
Hint  -  Solution

92. Consecutive integer sums (4 star)

In how many ways can 50! be expressed as a sum of two or more consecutive positive integers?

Hint  -  Answer  -  Solution

93. Pascal's triangle (4 star)

Show that any two elements (both greater than one) drawn from the same row of Pascal's triangle have greatest common divisor greater than one.  For example, the greatest common divisor of 28 and 70 is 14.

                1
              1   1
            1   2   1
          1   3   3   1
        1   4   6   4   1
      1   5  10  10   5   1
    1   6  15  20  15   6   1
  1   7  21  35  35  21   7   1
1   8  28  56  70  56  28   8   1
Hint  -  Solution

94. Square endings (4 star)

Find all 8-digit natural numbers n such that n2 ends in the same 8 digits as n.  Numbers are written in standard decimal notation, with no leading zeroes.

Hint  -  Answer  -  Solution

95. Integer polynomial (1 star)

Let P be a polynomial with integer coefficients.  If a, b, c are distinct integers, show that

cannot be satisfied simultaneously.

Hint  -  Solution

96. Five real numbers (3 star)

The sum of five real numbers is 7; the sum of their squares is 10.  Find the minimum and maximum possible values of any one of the numbers.

Hint  -  Answer  -  Solution

97. Two squares (2 star)

Find all pairs of positive integers, x, y, such that x2 + 3y and y2 + 3x are both perfect squares.

Hint  -  Answer  -  Solution

98. Three powers (3 star)

Find all solutions of 3x + 4y = 5z, for integers x, y, and z.

Hint  -  Answer  -  Solution

99. Two similar triangles (3 star)

Two similar triangles with integral sides have two of their sides the same.  If the third sides differ by 20141, find all of the sides.

Hint  -  Answer  -  Solution

100. Perpendicular medians (1 star)

Suppose the medians AA' and BB' of triangle ABC intersect at right angles.  If BC = 3 and AC = 4, what is the length of side AB?

Triangle ABC, with perpendicular medians AA' and BB'.
Hint  -  Answer  -  Solution

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Nick Hobson
nickh@qbyte.org
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Last updated: March 4, 2005