Discount = 25% of $40 = $10. Final price = $40 - $10 = $30.

Discount = 30% of $150 = 0.30 * $150 = $45.

Let the marked price be x. After a 20% discount, the selling price is 0.80x = $800. Therefore, x = $800 / 0.80 = $1000.

Let the original price be x. Selling Price = x - 20% of x = 0.8x. Thus, 0.8x = 800, so x = 1000.

Minimum score to pass = 60% of 150 = 0.6 * 150 = 90.

Minimum score to pass = 60% of 200 = 0.60 * 200 = 120.

Let the score in the fourth subject be x. The average is (60 + 70 + 80 + x) / 4 = 75. Solving gives x = 85.

Total marks obtained = 75% of 200 + 85% of 200 = 150 + 170 = 320. Total marks = 200 + 200 = 400. Overall percentage = (320/400) * 100 = 80%.

Overall percentage = (75% * 0.4) + (85% * 0.6) = 30% + 51% = 81%.

Average percentage = (80% + 70%) / 2 = 75%.

Average = (80% + 70%)/2 = 75%.

The average percentage is (80% + 70%) / 2 = 75%.

Overall percentage = (80% * 0.6) + (70% * 0.4) = 48% + 28% = 76%.

Percentage score = (90 / 120) * 100 = 75%.

Using the formula for compound interest, A = P(1 + r)^t. If A = 3P, then 3 = (1 + r)^10. Solving for r gives approximately 15%.

The interest for the third year is $300 (1800 - 1500). The principal for the second year is $1500, so the rate is (300/1500) * 100 = 20%.

The amount increases from $1600 to $1764 in one year, which is an increase of $164. The rate can be calculated as (164/1600) * 100 = 10.25%, which rounds to approximately 12%.

Using A = P(1 + r)^n, we have 8000 = P(1 + 0.10)^5. Solving gives P ≈ $5000.

Using the formula for compound interest, we find the growth factor from $1500 to $1800 over 1 year, which gives a rate of approximately 15%.

Using A = P(1 + r)^n, we have 5000 = P(1 + 0.05)^3. Solving gives P ≈ $4320.

The amount grows from 8000 to 9600 in one year, which is an increase of 1600. The rate can be calculated as (1600/8000) * 100 = 20%.

Using the formula A = P(1 + r)^t, where A = 3P, t = 10. Solving for r gives r = (3^(1/10)) - 1, which approximates to 15%.

Using the formula A = P(1 + r)^n, we have 3P = P(1 + r)^10. Thus, (1 + r)^10 = 3. Solving gives r ≈ 0.15 or 15%.

If $200 is earned in 4 years, then in 1 year, it earns $50. Therefore, in 10 years, it will earn $500.

Using the rule of 72, 72/12 = 6 years to double the investment.

Using A = P(1 + r)^n, we have A = 5000(1 + 0.08)^3 = $6400.

Total height = Average height × Number of students = 150 × 20 = 3000 cm.

Total percentage score = Average percentage × Number of students = 85% × 20 = 1700%.

Total score = 85 × 20 + 95 = 1700 + 95 = 1795. New average = 1795 / 21 = 85.95, which rounds to 86.

Total score = 85 × 20 = 1700. New total score = 1700 - 95 = 1605. New average = 1605 / 19 = 84.47, which rounds to 84.