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Question

Two coins are simultaneously tossed. The probability of two heads simultaneously appearing is

The correct answer is

1/4

Coin Toss Outcomes and Sample Space

When two coins are simultaneously tossed, we need to determine all the possible results that can occur. This collection of all possible results is known as the sample space.

Let 'H' represent a head and 'T' represent a tail. When tossing two coins, the outcomes for each coin are independent. The possible combinations are:

  • The first coin lands on Heads (H) and the second coin lands on Heads (H). This outcome is denoted as HH.
  • The first coin lands on Heads (H) and the second coin lands on Tails (T). This outcome is denoted as HT.
  • The first coin lands on Tails (T) and the second coin lands on Heads (H). This outcome is denoted as TH.
  • The first coin lands on Tails (T) and the second coin lands on Tails (T). This outcome is denoted as TT.

Therefore, the complete sample space (\(S\)) for tossing two coins simultaneously is:

\(S = \{HH, HT, TH, TT\}\)

The total number of possible outcomes in the sample space is \(n(S) = 4\).

Probability of Two Heads Appearing

We are interested in the event where two heads appear simultaneously. Let's call this event \(E\).

From our sample space \(S = \{HH, HT, TH, TT\}\), the outcome that consists of two heads appearing is only \(HH\).

So, the event \(E = \{HH\}\).

The number of favorable outcomes for event \(E\) is \(n(E) = 1\).

Calculating Probability

The probability of an event is calculated using the formula:

\[ P(E) = \frac{\text{Number of favorable outcomes for event E}}{\text{Total number of possible outcomes in the sample space}} = \frac{n(E)}{n(S)} \]

Using the values we found:

  • Number of favorable outcomes (\(n(E)\)) = 1 (for HH)
  • Total number of possible outcomes (\(n(S)\)) = 4 (for HH, HT, TH, TT)

Now, substitute these values into the probability formula:

\[ P(\text{two heads}) = \frac{1}{4} \]

Thus, the probability of two heads simultaneously appearing when two coins are tossed is \(1/4\).

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Important Questions from Types of Probability

  1. If f(x) is a probability density on the real line, then which of the following is NOT a valid probability density?

  2. The probability of student A passing an exam is 2/7 and that of B passing is 5/7. If these probabilities are independent, what is the probability that only B passes the examination

  3. A die is tossed three times, What is the probability of getting an odd number at least once ?

  4. There are two containers, with one containing 4 Red and 3 Green balls and the other containing 3 Blue and 4 Green balls. One ball is drawn at random from each container. The probability that one of the balls is Red and the other is Blue will be
  5. Given a fair six-faced dice where the faces are labelled ‘1’, ‘2’, ‘3’, ‘4’, ‘5’, and ‘6’, what is the probability of getting a ‘1’ on the first roll of the dice and a ‘4’ on the second roll?

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