Answer:
A large equilateral triangle pyramid stands in front of the city's cultural center. Each side of the base measures 40 feet and the slant height of each lateral side of the pyramid is 50 feet.
A painter can paint 100 square feet of the pyramid in 18 minutes.
How long does it take the painter to paint 75% of the pyramid?
Explanation:
The total surface area of the pyramid can be calculated using the formula for the lateral surface area of a pyramid:
Lateral surface area = (1/2) × perimeter of base × slant height
Since the base is an equilateral triangle, the perimeter is 3 times the length of one side:
Perimeter of base = 3 × 40 feet = 120 feet
Lateral surface area = (1/2) × 120 feet × 50 feet = 3000 square feet
To paint 75% of the pyramid, the painter needs to paint:
0.75 × 3000 square feet = 2250 square feet
Since the painter can paint 100 square feet in 18 minutes, the time required to paint 2250 square feet can be calculated as:
2250 square feet ÷ 100 square feet per 18 minutes = 225 ÷ 10 × 18 minutes = 405 minutes
Therefore, the painter would need 405 minutes or 6 hours and 45 minutes to paint 75% of the pyramid.