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
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