(Viva Voce) Chap 9 Exercise 9 Question 2


Average Speed = Distance/Time

(a) Average speed of Car X=60km/45mins=1⅓km/min
Ans: 80km/h

(b) Average speed of Car Y = (60/80*72)km/h
= 54km/h
Ans: 54km/h

(c) Average Speed of Car X : Average speed of Car Y
80 : 54
40 : 27

Ans: 40:27


  1. mathematical terms: 1
    Explanation of working/solution must be clear: 2
    understanding of concepts: 2
    accuracy of answer: 2

    you did well~!

  2. accuracy of answer[2]
    mathematical term[1]
    explanation of working/solution[3]
    understanding of concept[2]
    presentation[2]( unable to see the working on the paper)

  3. 1. It is good that you inform the audience the formula you are using to solve the problem. However, note that "Average Speed" is equal to "TOTAL distance travelled" over "TOTAL time taken".

    2. Instead of reading it as "k""m", it should be read as "kilometres".

    3. You are clear that if finding speed in "km/min", we should convert it to "km/h". However, you could further elaborate how to convert the speed in "km/min" to "km/h"

    4. When converting "1 h 20 min" to "h", why take 60 divided by 80? Should it be the other way, when 80 is divided by 60?

    5. Good, you used the term "reduce" the ratio. You could tell us how you reduce? For instance, as 2 is the common factor of the two average speeds, so, we divide the two numbers by 2 in order to get the simplest ratio.

    On the whole, it's clear.
    Good effort :)