Let the original price be x. Then, x - 0.2x = 40, which gives 0.8x = 40. Thus, x = 40 / 0.8 = $50.

Circumference = 2πr = 2 × 3.14 × 7 cm = 43.96 cm.

Let A's age be 3x and B's age be 4x. Then, 3x + 4x = 28, so 7x = 28, giving x = 4. Thus, A's age = 3x = 12.

Let A's age be 3x and B's age be 4x. Then, 3x + 4x = 70, giving 7x = 70, so x = 10. Thus, A's age = 3x = 30.

If the shorter side is 9 cm and the ratio is 3:4, then the longer side is (4/3) × 9 cm = 12 cm.

The third angle can be found by subtracting the sum of the other two angles from 180 degrees: 180 - (50 + 70) = 60 degrees.

The sum of the first n natural numbers is given by the formula n(n + 1)/2 = 255. Solving n(n + 1) = 510, we find n = 16.

Let the two numbers be x and y. We have x + y = 15 and xy = 50. Solving these equations gives the larger number as 10.

Let the other number be x. Then, x + 12 = 20. So, x = 20 - 12 = 8.

Let the numbers be x and y. We have x + y = 30 and x - y = 10. Solving these gives x = 20 and y = 10.

Relative error = (Uncertainty / Measured value) * 100 = (0.5 / 50.0) * 100 = 1%.

Substituting x = 3 into the expression: 2(3^2) + 3(3) - 5 = 2(9) + 9 - 5 = 18 + 9 - 5 = 22.

Maximum possible mass = Measured mass + Uncertainty = 2.50 kg + 0.05 kg = 2.55 kg.

In a triangle, the sum of angles is 180 degrees. If one angle is 90 degrees, the other two angles must sum to 90 degrees. Therefore, each of the equal angles is 45 degrees.

The number 100.0 has 1 decimal place, so the answer should also be rounded to 1 decimal place.

The number with the least decimal places is 0.3 (1 decimal place), so the answer should be rounded to 1 decimal place.

The result of 3.4567 + 2.1 is 5.5567. However, since 2.1 has only 2 significant figures after the decimal, the result should be rounded to 5.6, which has 3 significant figures.

The number 3.4567 has 4 significant figures. The leading digit is not counted as significant.

To find x, subtract 5 from both sides: 3x = 20 - 5 = 15. Then divide by 3: x = 15 / 3 = 5.

To solve for x, subtract 2x from both sides: 3x - 2x = 10 - 5, which simplifies to x = 5.

The term 2.1 × 10^2 has 2 significant figures, so the final answer should be rounded to 2 significant figures.

Substituting x = 2 into the equation gives 5(2) + 3y = 15, which simplifies to 10 + 3y = 15. Thus, 3y = 5, and y = 5/3.

Substituting x = 2 into the equation gives 5(2) + 3y = 20. This simplifies to 10 + 3y = 20, leading to 3y = 10, thus y = 10/3, which is approximately 3.33. The closest integer option is 4.

2.5 has 2 significant figures and 3.456 has 4 significant figures. The result should be rounded to 2 significant figures, giving 8.6.

Expanding gives 2x - 6 = 8. Adding 6 gives 2x = 14, thus x = 7.

Adding 4 to both sides gives 2x = 14. Dividing by 2 gives x = 7.

Subtracting 8 from both sides gives 4x = 16. Dividing by 4 gives x = 4.

Adding 8 to both sides gives 4x = 8. Dividing by 4 gives x = 2.

Calculating gives 12 + 15 = 27, and then 27 - 7 = 20.

Following the order of operations, first calculate 3 × 2 = 6. Then, 12 - 6 + 4 = 10.