# Puzzles

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#### Sunday Afternoon Maths LXVII

Coloured weightsNot Roman numerals

#### Advent calendar 2018

#### Sunday Afternoon Maths LXVI

Cryptic crossnumber #2#### Sunday Afternoon Maths LXV

Cryptic crossnumber #1Breaking Chocolate

Square and cube endings

List of all puzzles

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odd numbers dodecagons addition calculus prime numbers square roots sport cards chalkdust crossnumber speed regular shapes planes games perfect numbers clocks differentiation algebra doubling spheres time quadratics area complex numbers factors ellipses menace advent surds graphs routes partitions triangle numbers pascal's triangle 2d shapes factorials shape coordinates indices probability coins colouring probabilty floors remainders star numbers grids symmetry balancing crossnumbers lines wordplay trigonometry ave fractions unit fractions logic perimeter dates square numbers sum to infinity folding tube maps cube numbers number 3d shapes hexagons geometry proportion christmas irreducible numbers numbers shapes averages division digits means multiplication rectangles multiples crosswords integration sums functions squares percentages dice circles mean cryptic crossnumbers chess palindromes chocolate bases arrows taxicab geometry parabolas cryptic clues people maths rugby money triangles books polygons angles scales sequences integers volume## 2 December

What is the maximum number of lines that can be formed by the intersection
of 30 planes?

## Two lines

Let A and B be two straight lines such that the gradient of A is the y-intercept of B and the y-intercept of A is the gradient of B (the gradient and y-intercept of A are not the same). What are the co-ordinates of the point where the lines meet?