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

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Question 9:

(i) A lot of bulbs contains 4 defective ones. One bulb is drawn at random from the lot. What is the probability that this bulb is defective?

(ii) Suppose the bulb drawn in (i) is not defective and is not replaced. Now one bulb is drawn at random from the rest. What is the probability that this bulb is not defective?

Answer:

(i) Total number of favourable outcomes

Number of favourable outcomes

Hence P (getting a defective bulb)

(ii) Now total number of favourable outcomes

Number of favouroable outcomes

Hence P (getting a non-defective bulb)

Question 10:

A box contains discs which are numbered from to . If one disc is drawn at random from the box, find the probability that it bears (i) a two-digit number

(ii) a perfect square number

(iii) a number divisible by 5.

Answer:

Total number of favourable outcomes

(i) Number of two-digit numbers from 1 to are

Favourable outcomes

Hence, P (getting a disc bearing a two-digit number)

(ii) From 1 to 90, the perfect squares are and 81.

Favourable outcomes

Hence P (getting a perfect square)

(iii) The numbers divisible by 5 from 1 to 90 are 18.

Favourable outcomes

Hence P (getting a number divisible by 5)

Question 11:

A child has a die whose six faces show the letters as given below:

A, B, C, D, E, A

The die is thrown once. What is the probability of getting:

(i) A?

(ii) D?

Answer:

Total number of favourable outcomes

(i) Number of favourable outcomes

Hence P (getting a letter A)

(ii) Number of favourable outcomes

Hence P (getting a letter D)

Question 12:

Suppose you drop a die at random on the rectangular region shown in the figure given on the next page. What is the probability that it will land inside the circle with diameter ?

The Circle with Diameter

Answer:

Total area of the given figure (rectangle) And Area of circle

Hence, P(die to land inside the circle)

Question 13:

A lot consists of ball pens of which are defective and the others are good. Nuri will buy a pen if it is good, but will not buy if it is defective. The shopkeeper draws one pen at random and gives it to her. What is the probability that:

(i) She will buy it?

(ii) She will not buy it?

Answer:

Total number of favourable outcomes

(i) Number of non-defective pens

Number of favourable outcomes

Hence P (she will buy) (a non-defective pen)

(ii) Number of favourable outcomes

Hence