To find the volume of the scuba diving lagoon, we can divide it into three sections: the top rectangle, the middle section, and the bottom section.
The volume of the top rectangle can be found by multiplying the length (50 ft) by the width (20 ft) and the depth (0 ft, since it is at the top):
Volume of top rectangle = 50 ft * 20 ft * 0 ft = 0 ft³
The volume of the middle section can be found by multiplying the area of the rectangle (50 ft * 20 ft) by the depth (25 ft):
Volume of middle section = 50 ft * 20 ft * 25 ft = 25,000 ft³
The volume of the bottom section can be found by dividing the volume of the middle section by 2, since it is an upside-down pyramid:
Volume of bottom section = 25,000 ft³ / 2 = 12,500 ft³
Therefore, the total volume of the scuba diving lagoon is:
Total volume = Volume of top rectangle + Volume of middle section + Volume of bottom section
= 0 ft³ + 25,000 ft³ + 12,500 ft³
= 37,500 ft³
Therefore, the closest answer is 37,500 ft³.