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If a parachutist lands at a random point on a line between markers \(A\) and \(B\), find the probability that she is closer to \(A\) than to \(B\). Find the probability that her distance to \(A\) is more than three times her distance to \(B\).

Short Answer

Expert verified
The probabilities are \(\frac{1}{2}\) and \(\frac{1}{4}\).

Step by step solution

01

Understanding the problem

We need to calculate two probabilities: \(P(X < \frac{1}{2})\) which represents the parachutist being closer to \(A\) than \(B\), and \(P(X < \frac{1}{4})\) which represents her distance to \(A\) being more than three times her distance to \(B\).
02

Define coordinates

Place point \(A\) at coordinate \(0\) and \(B\) at coordinate \(1\) on a number line. The parachutist lands at a point \(X\), where \(0 \leq X \leq 1\).
03

Calculate the first probability

For the parachutist to be closer to \(A\) than \(B\), \(X\) must satisfy \(X < \frac{1}{2}\). Since \(X\) is uniformly distributed over the interval \([0, 1]\), the probability \(P(X < \frac{1}{2}) = \frac{1}{2}\).
04

Calculate the second probability condition

For the parachutist's distance to \(A\) to be more than three times her distance to \(B\), the condition is \(X > 3(1 - X)\).
05

Solve the second probability condition

The inequality \(X > 3 - 3X\) rearranges to \(4X > 3\), so \(X > \frac{3}{4}\). Thus, the probability \(P(X > \frac{3}{4}) = 1 - \frac{3}{4} = \frac{1}{4}\) since \(X\) is uniformly distributed.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Uniform Distribution
Uniform distribution is a type of probability distribution in which all outcomes are equally likely.
This means each value in the range has the same probability of occurring. In our problem, the parachutist landing anywhere between markers \(A\) and \(B\) is uniformly distributed, indicating that any point on the line between them is equally possible.

For a uniform distribution over an interval \([a, b]\), the probability of landing on any specific segment within that range can be found by looking at the length of the interval segment and dividing it by the total length \(b - a\).
In our problem, \(a = 0\) and \(b = 1\), making the length of the full range \(1 - 0 = 1\).
  • For her to be closer to \(A\) than \(B\) would mean her landing point \(X\) satisfies \(X < \frac{1}{2}\).
  • This is right in the middle of the distribution, so the segment of the range where this is true is \([0, \frac{1}{2}]\), which is half of the entire range.
This results in a probability of \(\frac{1}{2}\), reflecting an equally distributed likelihood of landing either closer to \(A\) or \(B\).
When probabilities are evenly spread, computations are simplified, and events have predictable probabilities, as shown here.
Inequality Solutions
Solving inequalities is key in probability, especially when determining specific conditions or sub-ranges of an interval.
The task requires analyzing conditions like when the parachutist's distance to \(A\) is more than three times her distance to \(B\).
This boils down to solving an inequality to find the part of the line where this condition holds.

The initial inequality fomulated is \(X > 3(1 - X)\), representing this specific condition.
To solve it:
  • Expand the brackets: \(X > 3 - 3X\)
  • Rearrange to gather terms with \(X\) on one side, which gives \(4X > 3\)
  • Divide both sides by 4, leaving \(X > \frac{3}{4}\)
This tells us the parachutist lands on segments greater than \(\frac{3}{4}\) of the entire line.
Given the usual uniform distribution assumption, this allows deriving probabilities through basic ratio calculations,
which is why the probability of this inequality being satisfied is \(\frac{1}{4}\), calculated as \(1 - \frac{3}{4}\).
Random Points
A random point in probability theory often refers to a location or value selected unpredictably within a given domain.
Here, the parachutist lands randomly on a line between points \(A\) and \(B\), understood as selecting a point \(X\) from the interval \([0, 1]\).

Random selection implies no pattern or bias towards any particular area of the line,
affirming the use of a uniform distribution where all segments of the line are equally likely to host the random point.
This concept simplifies solving probabilistic problems, as discussed.
  • For instance, finding the probability that the parachutist lands closer to one end depends simply on the length of the half-segment considered.
  • The solution involves geometric reasoning and calculating intersections of random ranges with defined conditions, like comparisons of distances to \(A\) and \(B\).
By understanding how random points are placed within a certified distribution,
we can more easily employ methods such as inequality solution for conditions like the parachutist's role,
offering logical, clear insights into probability-focused problems.

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Most popular questions from this chapter

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