Probability of Single Events practice questions

Secondary 2 topics, working towards the O-Level Mathematics 4052 syllabus. Every question below has a full worked solution.

When a student gets a question wrong in Math Amigo, it does not show the answer straight away. It reads the working, identifies the step that went wrong, and asks a question that points at the correction. The worked solution is there once a genuine attempt has been made.

Practise probability of single events free

What this topic covers

Worked examples

Example 1

A drawer contains 4 orange, 7 white and 6 red socks. A sock is drawn at random. Find the probability of drawing a sock that is not red. Give your answer as a fraction in its simplest form.
Show the worked solution
  • $\text{Total number of socks} = 4 + 7 + 6$
  • $= 17$
  • $\text{Number of favourable outcomes (not red)} = 11$
  • $P(\text{not red}) = \frac{11}{17}$
  • $= \frac{11}{17}$

Answer: 11/1711/17

Example 2

A circle is divided into sectors of different colours. The angles of the grey, white, green sectors are 270°270°, 30°30°, 30°30° respectively. Find the angle of the red sector.
Show the worked solution
  • $\text{Sum of known angles} = 270° + 30° + 30°$
  • $= 330°$
  • $\text{Angle of red sector} = 360° - 330°$
  • $= 30°$

Answer: 3030

Example 3

A box contains <i>x</i> red marbles, (x+4)(x + 4) orange marbles and 99 green marbles. A marble is drawn at random. The probability of drawing an orange marble is 37\frac{3}{7}. Find the value of <i>x</i>.
Show the worked solution
  • Total $= x + (x + 4) + 9$
  • $= 2x + 13$
  • $P(\text{orange}) = \frac{x + 4}{2x + 13}$
  • $\frac{x + 4}{2x + 13} = \frac{3}{7}$
  • $7(x + 4) = 3(2x + 13) \quad \scriptsize\textit{cross multiply}$
  • $7x + 28 = 6x + 39$
  • $x = 11$

Answer: 1111

Questions parents ask

Is it really free?

The free plan is permanent and does not ask for a card. It has daily limits on the AI feedback, and the paid plans lift them.

Which syllabus does this follow?

O-Level Mathematics (4052), for Singapore secondary students. Math Amigo covers Secondary 1 to 4, both O-Level Mathematics and Additional Mathematics.

Will it just show my child the answer?

No. On a wrong answer it looks at the working, points to the step that went wrong, and asks a question that helps the student find the correction. The full worked solution is available after a genuine attempt.

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