Simultaneous equations

problem

Double Time

Age

16 to 18

Challenge level

Crack this code which depends on taking pairs of letters and using two simultaneous relations and modulus arithmetic to encode the message.
problem

Table Height

Age

14 to 16

Challenge level

A table has blocks of wood placed on and next to it. Can you work out how tall it is?
problem

Packing Boxes

Age

14 to 16

Challenge level

Look at the times that Harry, Christine and Betty take to pack boxes when working in pairs, to find how fast Christine can pack boxes by herself.
problem

Pareq Calc

Age

14 to 16

Challenge level

Triangle ABC is an equilateral triangle with three parallel lines going through the vertices. Calculate the length of the sides of the triangle if the perpendicular distances between the parallel lines are 1 unit and 2 units.
problem

Walls

Age

16 to 18

Challenge level

Plane 1 contains points A, B and C and plane 2 contains points A and B. Find all the points on plane 2 such that the two planes are perpendicular.
problem
Favourite

Fruity Totals

Age

7 to 16

Challenge level

In this interactivity each fruit has a hidden value. Can you deduce what each one is worth?
problem
Favourite

Letter Land

Age

11 to 14

Challenge level

If: A + C = A; F x D = F; B - G = G; A + H = E; B / H = G; E - G = F and A-H represent the numbers from 0 to 7 Find the values of A, B, C, D, E, F and H.
problem

Colour Islands Sudoku

Age

11 to 14

Challenge level

An extra constraint means this Sudoku requires you to think in diagonals as well as horizontal and vertical lines and boxes of nine.
problem

Addition Equation Sudoku

Age

11 to 14

Challenge level

You need to find the values of the stars before you can apply normal Sudoku rules.
problem

The Simple Life

Age

11 to 14

Challenge level

The answer is $5x+8y$... What was the question?