Work done = Number of workers * Number of days. If 5 workers take 10 days, then 10 workers will take 10/2 = 5 days.

Profit = Selling Price - Cost Price = 100 - 80 = $20.

Profit = Selling Price - Cost Price = 50 - 40 = 10. Profit Percentage = (10/40) * 100 = 25%.

Let the number of girls be x. Then, 3/2 = 30/x => x = (2/3) * 30 = 20.

Simple Interest = Principal * Rate * Time / 100. Therefore, Principal = (200 * 100) / (5 * 2) = $2000.

15% of 300 is calculated as (15/100) * 300 = 45.

Compound Interest = P(1 + r/n)^(nt) - P = 1000(1 + 0.05/1)^(1*2) - 1000 = 1000(1.1025) - 1000 = 102.50.