Discount = 10% of 200 = 20. Selling Price = Marked Price - Discount = 200 - 20 = $180.

Let the original price be x. Then, x - 0.2x = 120, 0.8x = 120, x = 120 / 0.8 = $150.

Let Cost Price = x. Selling Price = x + 0.5x = 1.5x. 1.5x = 30, x = 30 / 1.5 = $20.

Using the formula A = P(1 + r)^t, if A = 2P, then 2 = (1 + r)^5. Solving gives r = 10%.

Speed in km/h = 150 km / 3 h = 50 km/h. To convert to m/s, multiply by (1000 m / 1 km) * (1 h / 3600 s) = 50 * (1000/3600) = 13.89 m/s.

Average Speed = Total Distance / Total Time = 300 km / 5 h = 60 km/h.

Percentage Increase = [(New Population - Old Population) / Old Population] × 100 = [(25000 - 20000) / 20000] × 100 = 25%.

Let the number of boys be 3x and girls be 2x. Then, 3x + 2x = 30, which gives 5x = 30, so x = 6. Therefore, the number of girls is 2x = 12.

Let the number of boys be 3x and girls be 4x. Given 4x = 28, we find x = 7. Thus, boys = 3x = 3*7 = 21.

15% of 200 is calculated as (15/100) * 200 = 30.

25% of 200 is calculated as (25/100) * 200 = 50.

Average = (10 + 20 + 30 + 40 + 50) / 5 = 150 / 5 = 30.

The GCD of 24 and 36 can be found by listing the factors: 24 = 2^3 * 3, 36 = 2^2 * 3^2. The GCD is 2^2 * 3 = 12.

The LCM of two numbers is found by taking the highest power of each prime factor. The prime factorization of 12 is 2^2 * 3 and for 15 is 3 * 5. Thus, LCM = 2^2 * 3 * 5 = 60.

The first 4 prime numbers are 2, 3, 5, and 7. Their product is 2 * 3 * 5 * 7 = 210.

The first 5 prime numbers are 2, 3, 5, 7, and 11. Their product is 2 * 3 * 5 * 7 * 11 = 2310.

The first three prime numbers are 2, 3, and 5. Their product is 2 * 3 * 5 = 30.

The square root of 144 is 12, since 12 * 12 = 144.

The sum of the first n natural numbers is given by the formula n(n + 1)/2. For n = 10, the sum is 10(10 + 1)/2 = 10 * 11 / 2 = 55.

Calculating 7^2 = 49 and 3^2 = 9. Therefore, 49 + 9 = 58.