Ratio and proportion

A new problem posed by Lyndon Baker who has devised many NRICH problems over the years.

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

A male punky fish has 9 stripes and a female punky fish has 8 stripes. I count 86 stripes on the fish in my tank. What is the ratio of male fish to female fish?

Malcolm and Nikki run at different speeds. They set off in opposite directions around a circular track. Where on the track will they meet?

When a mixture of gases burn, will the volume change?

Ever wondered what it would be like to vaporise a diamond? Find out inside...

A brief introduction to PCR and restriction mapping, with relevant calculations...

Three-quarters of the junior members of a tennis club are boys and the rest are girls. What is the ratio of boys to girls among these members?

Two motorboats travelling up and down a lake at constant speeds leave opposite ends A and B at the same instant, passing each other, for the first time 600 metres from A, and on their return, 400 metres from B. How long is the lake?

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