To solve this problem, we can use a concept called the "Frobenius coin problem." In this problem, we want to find the largest number that cannot be expressed as a sum of multiples of given numbers.

In this case, the given numbers are 6, 9, and 20. We want to find the largest number of bitterballs that cannot be ordered in these portions.

Let's analyze the given options:

Option A) 43 - This option is the correct answer. We can express 43 as a sum of multiples of 6, 9, and 20. For example, we can order 6 bitterballs (6 * 7 = 42) and add an extra 1 bitterball to make a total of 43.

Option B) 46 - We can express 46 as a sum of multiples of 6, 9, and 20. For example, we can order 9 bitterballs (9 * 5 = 45) and add an extra bitterball to make a total of 46.

Option C) 76 - We can express 76 as a sum of multiples of 6, 9, and 20. For example, we can order 20 bitterballs (20 * 3 = 60), 9 bitterballs (9 * 1 = 9), and 6 bitterballs (6 * 1 = 6) to make a total of 76.

Option D) 79 - We can express 79 as a sum of multiples of 6, 9, and 20. For example, we can order 20 bitterballs (20 * 3 = 60), 9 bitterballs (9 * 1 = 9), and 6 bitterballs (6 * 1 = 6) to make a total of 79.

Therefore, the correct answer is option A) 43. This option is correct because it is the largest number that cannot be ordered in portions of 6, 9, or 20.

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To find the average speed for the complete journey, we need to calculate the total distance traveled and the total time taken.

Let's assume the total distance traveled is "d" km.

The first half of the distance is d/2 km, and the salesman drives at a constant speed of 80 km/h for this distance. So, the time taken for the first half is (d/2) / 80 = d/160 hours.

The second half of the distance is also d/2 km, and the salesman drives at a constant speed of 120 km/h for this distance. So, the time taken for the second half is (d/2) / 120 = d/240 hours.

The total time taken for the complete journey is the sum of the time taken for the first half and the time taken for the second half:

Total time = d/160 + d/240 = (3d + 2d) / (3 * 160) = 5d / 480 = d / 96 hours.

The average speed is calculated by dividing the total distance traveled by the total time taken:

Average speed = Total distance / Total time = d / (d/96) = 96 km/h.

Therefore, the correct answer is D) none of these, as the salesman's average speed for the complete journey is 96 km/h.

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To solve this problem, we can use the concept of a right triangle and the Pythagorean theorem.

Let's assume that the distance between the two pillars is "x" meters.

We can form a right triangle with the cable as the hypotenuse, one pillar as the base, and the ground as the height. The other pillar will also have the same height.

Using the Pythagorean theorem, which states that in a right triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides, we can write the following equation:

$x^2 = 15^2 - 7^2$

$x^2 = 225 - 49$

$x^2 = 176$

Taking the square root of both sides, we get:

$x = \sqrt{176}$

$x \approx 13.26$

Therefore, the distance between the two pillars is approximately 13.26 meters.

Since none of the given options match the correct answer, we can conclude that the correct answer is D) None of these.

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