A reservoir's water level decreased by $20\%$ over the summer due to evaporation. If the water level is currently at $120$ million liters, how much water was there initially?

• A. $24$ million liters
• B. $150$ million liters.
• C. $96$ million liters.
• D. $30$ million liters.

Answer: (B)

Verified step by step guidance

1. Let the initial water level in the reservoir be represented by the variable \(I\) (in million liters).
2. Since the water level decreased by 20%, the current water level is 80% of the initial level. This can be written as the equation: \$0.80 \times I = 120$.
3. To find the initial water level \(I\), divide both sides of the equation by 0.80: \(I = \frac{120}{0.80}\).
4. Simplify the right side of the equation to express \(I\) in terms of a division operation.
5. The result from this division will give the initial water level in million liters before the evaporation occurred.