### (Viva Voce) Chap 9 Exercise 9 Question 4

(a) 600cm^3 = 5 units
Alcohol = 1 unit
= 600cm^3 ÷ 5
= 120cm^3

(b)Water = 4 units
= 4 x 120cm^3
= 480cm^3

(c) 4 units(old) = 3 units(new)
= 480cm^3
1 unit(new) = Alcohol
= 160cm^3
Amount of alcohol added = 160cm^3 - 120cm^3
= 40cm^3

1. Video cut off and not flip.Voice is very clear.
Presentation 1/2
Mathematical Terms 1/1
Explanation of working 2/3
Understanding of concepts 2/2
Accuracy of answer 2/2
Total:7/10

2. 1. Good idea to go through the question to set the context.

2. The explanation for (a) is very clear, and you've chose to use the word "worth" :) Another more common word is "represent".

3. The unit should be read as "cubic centimetres" instead of "c""m" "cube".

4. The explanation of part (c) is clear. You draw our attention to the fact that "the "4" old units" is now "3" new units while the volume of water remains unchanged. Good :)

5. Visuals - it's a mirror image. Good to find out from classmates how they shot the clip.

6. For future viva voce, remember check that the full clip is recorded and uploaded :)