Conditional Probability (CIE IGCSE Maths: Extended)

Sonia has a bag containing 20 sweets.
In the bag, there are 5 red, 6 green and 9 yellow sweets.
Sonia chooses two sweets at random, without replacement, from the bag.

i)

Show that the probability that she chooses two green sweets is .

[2]

[4]

The heights, metres, of the 120 boys in an athletics club are recorded.
The table shows information about the heights of the boys.

Height ( metres)
Frequency	7	18	30	24	27	14

Three boys are chosen at random from the club.

Calculate the probability that one of the boys has a height greater than 1.8 m and the other two boys each have a height of 1.4 m or less.

200 students estimate the total area, , of the windows in the classroom.
The table shows their results.

Area (m2)
Frequency	32	64	80	24

Two students are chosen at random from those students that estimated the area of the windows to be more than .
 
Find the probability that one of the two students estimates the area to be greater than and the other student estimates the area to be  or less.

{students in a school}
{students who play football}
{students who play baseball}
 
There are 240 students in the school.
 
• 120 students play football
• 40 students play baseball 
• 90 students play football but not baseball.

Complete the Venn diagram to show this information.
 

Two students who play baseball are chosen at random.
 
Find the probability that they both also play football.

Talika has a bag which contains 10 red balls and 8 blue balls.
Talika takes three balls at random from her bag, without replacement.
 
Calculate the probability that the three balls are the same colour.

 
The Venn diagram above shows information about the number of students who study Music (M), Drama (D) and Geography (G).

Two students are chosen at random from those who study Drama.
 
Calculate the probability that they both also study Music.

A box contains 20 packets of potato chips.
6 packets contain barbecue flavoured chips.
10 packets contain salt flavoured chips.
4 packets contain chicken flavoured chips.
Maria takes two packets at random without replacement.

Find the probability that she takes two packets of different flavoured chips.

This year, 40 students have each travelled by one or more of plane (), train () or boat ().

7 have travelled only by plane.
11 have travelled only by train.
9 have travelled only by boat.

Complete the Venn diagram.

Two students are chosen at random.

Calculate the probability that they both have travelled only by plane.

Two students are chosen at random from those who have travelled by train.

Calculate the probability that they both have also travelled by plane.

A box contains 20 packets of potato chips.
6 packets contain barbecue flavoured chips.
10 packets contain salt flavoured chips.
4 packets contain chicken flavoured chips.
 
Maria takes three packets at random, without replacement, from the 20 packets.

Find the probability that she takes at least two packets of chicken flavoured chips.

The diagram shows two sets of cards.

Lena chooses three cards at random from Set C without replacement.

Find the probability that the third card chosen is numbered 4.