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. Identify the variables: Let the initial water level be \(x\) million liters. The water level decreased by 20%, so the current water level is 80% of the initial level.
2. Express the current water level in terms of the initial level: Since 20% was lost, the remaining water is \$100\% - 20\% = 80\%\( of the initial amount. This can be written as \)0.80 \times x$.
3. Set up the equation using the given current water level: \$0.80 \times x = 120$ million liters.
4. Solve for \(x\) by dividing both sides of the equation by 0.80: \(x = \frac{120}{0.80}\).
5. Interpret the result: The value of \(x\) you find will be the initial amount of water in the reservoir before the evaporation.