The concept is as follows:

To determine the ratio between two quantities of different species, the ratio between the measurements of these quantities is determined. This reason must be accompanied by the notation that relates the quantities involved.Examples:

**1)** **Average consumption:**

Beatriz went from São Paulo to Campinas (92Km) in her car. 8 liters of fuel were spent on this route. What is the ratio between distance and fuel consumed? What does this reason mean?

Reason =**Solution:**

Reason = (reads "11.5 kilometers per liter")

This reason means that for each liter consumed an average of 11.5 km was covered.

**2)** **Average speed:**

Moacir made the Rio-São Paulo route (450km) in 5 hours. What is the ratio between the measurement of these quantities? What does this reason mean?

Reason =**Solution:**

Reason =*90 km / h*(reads "90 kilometers per hour")

This reason means that the average hourly distance was 90 km.

**3)** **Demographic density:**

The state of Ceará in the last census had a population estimated at 6,701,924 inhabitants. Its area is 145,694 km

Reason =^{2}. Determine the ratio between the number of inhabitants and the area of this state. What does this reason mean?**Solution:**

Reason =*46 inhab / km*(reads "46 inhabitants per square kilometer")^{2}

This ratio means that in each square kilometer there are on average 46 inhabitants.

**4)** **Absolute density or specific mass:**

An iron cube with a 1cm edge has a mass of 7.8g. Determine the ratio between the mass and volume of this body. What does this reason mean?

Volume = 1cm. 1cm. 1cm = 1cm**Solution:**^{3}

Reason =

Reason =*7.8 g / cm*(reads "7.8 grams per cubic centimeter")^{3}

This ratio means that 1cm^{3}of iron weighs 7.8g.