CBSE Class 10-Mathematics: Chapter –15 Probability Part 4

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Question 17:

In a musical chair same the person playing the music has been advised to stop playing the music at any time within 2 minutes after she starts playing. What is the probability that the music will stop within the half minute after starting.

Answer:

Here the possible outcomes are all the numbers between .

This is the portion of the number line from as shown in figure.

Let A be the event that ‘the music is stopped within the first half minute. ‘Then, outcomes favourable to event A are all points on the number line from

The total number of outcomes are the points on the number line from i.e. ) to 2.

Question 18:

A jar contains marbles each of which is blue. Green or white. The probability of selecting a blue marble at random from the jar is and the probability of selecting a green marble at random is . How many white marbles does the jar contain?

Answer:

Let there be blue, g green and w white marbles in the marbles in the jar. Then, 4

It is given that the probability of selecting a blue marbale is .

We have.

Substituting the values of b and in (i), we get

1 Mark Questions

Question 1:

Complete the statements:

(i) Probability of event Probability of event “not E” _______________

(ii) The probability of an event that cannot happen is _______________. Such an event is called _______________.

(iii) The probability of an event that is certain to happen is _______________. Such an event is called _______________.

(iv) The sum of the probabilities of all the elementary events of an experiment is _______________.

(v) The probability of an event is greater than or equal to _______________ and less than or equal to _______________.

Answer:

(i)

(ii) , impossible event.

(iii) , sure or certain event

(iv)

(v)

Question 2:

Which of the following cannot be the probability of an event:

(A)

(B)

(C)

(D)

Answer:

(B) Since the probability of an event E is a number P(E) such that

cannot be the probability of an event.

Question 3:

If , what is the probability of ‘not E’?

Answer:

Since

Question 4:

It is given that in a group of students, the probability of students not having the same birthday is . What is the probability that the students have the same birthday?

Answer:

Let E be the event of having the same birthday

But