The price of coffee decreases by 25% and a person ends up consuming more coffee. If his expenditure on coffee increases by 20%, by what percentage did his consumption increase?

Given information:
- The price of coffee decreases by 25%
- The person's expenditure on coffee increases by 20%

To find the percentage increase in consumption, we need to analyze the relationship between the price, expenditure, and consumption.

Analysis:
Let's assume initially the person's expenditure on coffee was 100 units and the price per unit was 10 units. This means the person initially purchased 10 units of coffee.

After the price decrease of 25%, the new price per unit will be (10 - (25% of 10)) = 7.5 units.

Now, let's calculate the new expenditure on coffee after the price decrease and the consumption increase.

Step 1: Calculate the new price per unit
- Initial price per unit = 10 units
- Price decrease = 25%
- New price per unit = 10 - (25% of 10) = 7.5 units

Step 2: Calculate the new expenditure on coffee
- Initial expenditure = 100 units
- Price decrease = 25%
- New price per unit = 7.5 units
- New expenditure = (100 units) * (7.5 units) = 750 units

Step 3: Calculate the consumption increase
- Initial consumption = (Initial expenditure) / (Initial price per unit) = 100 units / 10 units = 10 units
- New consumption = (New expenditure) / (New price per unit) = 750 units / 7.5 units = 100 units

Step 4: Calculate the percentage increase in consumption
- Initial consumption = 10 units
- New consumption = 100 units
- Increase in consumption = (New consumption - Initial consumption) = 100 units - 10 units = 90 units
- Percentage increase in consumption = (Increase in consumption / Initial consumption) * 100 = (90 units / 10 units) * 100 = 900%

Therefore, the person's consumption increased by 900% due to the decrease in coffee price and the increase in expenditure.

Conclusion:
The person's consumption increased by 900% due to the 25% decrease in coffee price and the 20% increase in expenditure.