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Chapter 7: Probability [ckgubid/ AMF5 /W25 /Mon /KYRHG]Name:..

7.1 Probability of An Events

)()(

)(S n An

A P =

Examples

1. A letter is chosen from the word UNIVERSAL . Find the probability that the letter is a consonant.

2. Twenty cards, numbered from 21 to 40, are put in a bag. A card is drawn randomly from the bag. Findthe probability that the number on the card is a prime number.

3. The letters of the word

are written on eleven cards. If one card is drawn at random, what is the probability that the card has(a) the letter B?(b) a vowel?

4. A vase holds 6 stalks of red roses and k stalks of white roses. If a stalk of flower is picked randomly

from the vase, the probability of picking a white rose is52

, find the value of k .

5. A bag contains x blue marbles and )6( + x green marbles. If a marble is picked at random, the

probability of getting a blue marble is135

, find the number of green marbles.

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P R O B A B I L I T Y

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6. Table below shows the number of pens in a box.Colour Number of pens Blue 8 Black x Red x+ 7

Given that the probability of picking a black pen at random is113

. Calculate the total number of pens in

the box.

7. Table below shows the number of marbles in a basket.

Colour Black Blue Red Number of

marblesx y 6

The probability of picking a blue marble at random is31

and the probability of picking a black marble is

125

. Find the values of x and y.

8. A box contains red, blue and black pens. It is given that there are 30 red pens and 10 blue pens in the box.

(a) If the probability of choosing a red pen at random from the box is52

, find the number of pens in

the box.(b) Another 15 blue pens are added into the box, find the probability of choosing a black pen from the

box.

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