My recipe is for 12 cakes - how do I change it if I want to make a different number of cakes?

An article for teachers which discusses the differences between ratio and proportion, and invites readers to contribute their own thoughts.

A farmer is supplying a mix of seeds, nuts and dried apricots to a manufacturer of crunchy cereal bars. What combination of ingredients costing £5 per kg could he supply?

How long will it take Mary and Nigel to wash an elephant if they work together?

One night two candles were lit. Can you work out how long each candle was originally?

Scientists often require solutions which are diluted to a particular concentration. In this problem, you can explore the mathematics of simple dilutions

If it takes four men one day to build a wall, how long does it take 60,000 men to build a similar wall?

Is it cheaper to cook a meal from scratch or to buy a ready meal? What difference does the number of people you're cooking for make?

The triathlon is a physically gruelling challenge. Can you work out which athlete burnt the most calories?

Build a scaffold out of drinking-straws to support a cup of water

Imagine you were given the chance to win some money... and imagine you had nothing to lose...

A ladder 3m long rests against a wall with one end a short distance from its base. Between the wall and the base of a ladder is a garden storage box 1m tall and 1m high. What is the maximum distance. . . .

A right circular cone is filled with liquid to a depth of half its vertical height. The cone is inverted. How high up the vertical height of the cone will the liquid rise?

Two buses leave at the same time from two towns Shipton and Veston on the same long road, travelling towards each other. At each mile along the road are milestones. The buses' speeds are constant. . . .

In the ancient city of Atlantis a solid rectangular object called a Zin was built in honour of the goddess Tina. Your task is to determine on which day of the week the obelisk was completed.

Rectangle PQRS has X and Y on the edges. Triangles PQY, YRX and XSP have equal areas. Prove X and Y divide the sides of PQRS in the golden ratio.

What's the most efficient proportion for a 1 litre tin of paint?

In a race the odds are: 2 to 1 against the rhinoceros winning and 3 to 2 against the hippopotamus winning. What are the odds against the elephant winning if the race is fair?

A garrison of 600 men has just enough bread ... but, with the news that the enemy was planning an attack... How many ounces of bread a day must each man in the garrison be allowed, to hold out 45. . . .

The large rectangle is divided into a series of smaller quadrilaterals and triangles. Can you untangle what fractional part is represented by each of the ten numbered shapes?

Using an understanding that 1:2 and 2:3 were good ratios, start with a length and keep reducing it to 2/3 of itself. Each time that took the length under 1/2 they doubled it to get back within range.

A trapezium is divided into four triangles by its diagonals. Can you work out the area of the trapezium?

Which exact dilution ratios can you make using only 2 dilutions?

Which dilutions can you make using 10ml pipettes and 100ml measuring cylinders?

Construct a line parallel to one side of a triangle so that the triangle is divided into two equal areas.

At the beginning of the night three poker players; Alan, Bernie and Craig had money in the ratios 7 : 6 : 5. At the end of the night the ratio was 6 : 5 : 4. One of them won $1 200. What were the. . . .

Some of the numbers have fallen off Becky's number line. Can you figure out what they were?

Mike and Monisha meet at the race track, which is 400m round. Just to make a point, Mike runs anticlockwise whilst Monisha runs clockwise. Where will they meet on their way around and will they ever. . . .

When Charlie retires, he's looking forward to the quiet life, whereas Alison wants a busy and exciting retirement. Can you advise them on where they should go?

Can you work out how to produce different shades of pink paint?

Can you find an efficent way to mix paints in any ratio?

Can you fill in the mixed up numbers in this dilution calculation?

Read all about the number pi and the mathematicians who have tried to find out its value as accurately as possible.

Two perpendicular lines lie across each other and the end points are joined to form a quadrilateral. Eight ratios are defined, three are given but five need to be found.

Which is a better fit, a square peg in a round hole or a round peg in a square hole?

The area of a regular pentagon looks about twice as a big as the pentangle star drawn within it. Is it?

What is the ratio of the area of a square inscribed in a semicircle to the area of the square inscribed in the entire circle?

Two ladders are propped up against facing walls. The end of the first ladder is 10 metres above the foot of the first wall. The end of the second ladder is 5 metres above the foot of the second. . . .

Take any rectangle ABCD such that AB > BC. The point P is on AB and Q is on CD. Show that there is exactly one position of P and Q such that APCQ is a rhombus.

A circle of radius r touches two sides of a right angled triangle, sides x and y, and has its centre on the hypotenuse. Can you prove the formula linking x, y and r?

Triangle ABC is equilateral. D, the midpoint of BC, is the centre of the semi-circle whose radius is R which touches AB and AC, as well as a smaller circle with radius r which also touches AB and AC. . . .

The Earth is further from the Sun than Venus, but how much further? Twice as far? Ten times?

Two right-angled triangles are connected together as part of a structure. An object is dropped from the top of the green triangle where does it pass the base of the blue triangle?

If the sides of the triangle in the diagram are 3, 4 and 5, what is the area of the shaded square?

The scale on a piano does something clever : the ratio (interval) between any adjacent points on the scale is equal. If you play any note, twelve points higher will be exactly an octave on.

Straight lines are drawn from each corner of a square to the mid points of the opposite sides. Express the area of the octagon that is formed at the centre as a fraction of the area of the square.

Find the ratio of the outer shaded area to the inner area for a six pointed star and an eight pointed star.

The diagonals of a trapezium divide it into four parts. Can you create a trapezium where three of those parts are equal in area?

We use statistics to give ourselves an informed view on a subject of interest. This problem explores how to scale countries on a map to represent characteristics other than land area.