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A **compound measure** combines **two** units into one — like miles per hour or grams per cm³. Each is really a division of one quantity by another. The big three are **speed**, **density** and **pressure**. One formula-triangle trick handles them all. On your marks.

Speed = distance ÷ time 🚗

**Speed = distance ÷ time.** The **formula triangle** stores all three versions: put **D** on top, with **S** and **T** underneath. **Cover the one you want** and read off the rest: cover S → D over T (speed = distance ÷ time); cover D → S × T (distance = speed × time); cover T → D over S (time = distance ÷ speed).

Cover to find speed

An interactive activity.

Work out the speed

An interactive activity.

Order the method

An interactive activity.

Rearrange the triangle

A car travels at 5 m/s for 4 seconds. Which calculation gives the DISTANCE it covers?

• distance = speed × time = 5 × 4 = 20 m
• distance = speed ÷ time = 5 ÷ 4
• distance = time ÷ speed = 4 ÷ 5
• distance = speed + time = 5 + 4

Density = mass ÷ volume 🧊

**Density** tells you how much mass is packed into a volume: **Density = mass ÷ volume**, in units like **g/cm³**. It works with its own triangle (M on top, D and V below) exactly like speed. Careful: it is mass ÷ volume, never volume ÷ mass.

Work out the density

An interactive activity.

Pressure = force ÷ area 🔨

The third compound measure is **pressure**: **Pressure = force ÷ area**, measured in N/m² (also called pascals). Same triangle idea (F on top, P and A below). A large force on a small area gives a high pressure — which is why sharp knives cut so well.

Match each measure to its formula

Plot the position

An interactive activity.

The race rules

Speed is distance _____ time. Density is mass divided by _____. Before using a compound measure, make sure the two quantities are in matching _____.