(a) Go through Chapter 9 (p9 to p11)

(b) Attempt Exercise 9.2 Q1 to Q10

2. ACELearning Portal: eLearning Portal

- Subject: Secondary 1 Express
- Additional Arithmetic
- Ratio, Rate and Speed: Choose
**Rate**

**Rate, Average Rate, Example 1, Example 2**

(b) Try

**Practice Drills**on your own to check your understanding

(c) Attempt Acelearning Quiz:

**Chap 9.2 Rate Quiz 1**(This has been assigned to you on 1 May 2010).

**You are expected to complete Chapter 9.2 on your own by 15 May 2010.**

*As this chapter is not going to be covered in the class, please check/clarify with Ms Loh (Face-to-face or virtually) when you are in doubt or need help.*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Answers to Exercise 9.2**

**Basic Practice**

**No. 1**

(a) A 2 litre bottle of peanut oil costs $7

The price rate is

**$3.50 /l**

(b) A company produces 360 vases in 5 days

The rate of production is

**72 vases/day**

(c) Huili typed 376 words in 8 minutes

Her rate of typing is

**47 words/min**

(d) A carpet of area 3 m² costs $240.

The price rate is

**$80/m²**

(e) The mass of a 2.5-m metal bar is 10 kg

The rate of mass is

**4 kg/m**

(f) The mass of 12 eggs is 720g

The rate of mass is

**60g/egg**

**No. 2**

Rahman works 5 days a week and 8 hours a day. His daily wage is $184.

(a) Find his hourly wage rate.

**Since his daily wage is $184 and he works for 8 hours a day,**

**His hourly wage rate = $184 ÷ 8 = $23/h**

(b) Find his weekly wage rate.

**Since he works for 5 days a week,**

**His weekly wage rate = $184 x 5 = $920/week**

**No. 3**

A car travelled 225 km on 25 litres of petrol. The price of the petrol consumed was $30.

(a) Find the rate of petrol consumption in km/litre

**Since the car consumes 25 litres of petrol in 225 km**

**The rate of consumption (i.e. distance the car could travel with 1 litre of petrol)**

**= 225 km ÷ 25 litres**

**= 9 km/litre**

(b) What is the price of petrol per litre?

**Since 25 litres of petrol cost $30,**

**The price of petrol per litre = $30 ÷ 25**

**= $1.20/litre**

**No. 4**

There are 6 wooden cubes, each of side 5 cm. Their total mass is 525 g. Find the mass per

(a) cube

(b) cm³ of cube.

**(a) Mass of each cube = 525g ÷ 6**

**= 87.5 g**

**(b) Volume of each cube = 5 x 5 x 5 cm³**

**= 125 cm³**

**Hence, mass per cm³ of cube = 87.5g ÷ 125cm³**

**= 0.7 g/cm³**

**Further Practice**

**No. 5**

John spent $120 on 8 concert tickets

(a) Find the price per ticket

**Price per ticket = $120 ÷ 8**

**= $15**

(b) Find the price of 10 tickets

**Price of 10 tickets = $15 x 10**

**= $150**

**No. 6**

The price of laying 12 m² of floor tiles is $270.

(a) Find the price of laying floor tiles per m².

**Price of laying floor tiles per m² = $270 ÷ 12**

**= $22.50**

(b) Find the price of laying 20 m² of floor files.

**Price = $22.50 x 20**

**= $450**

**No. 7**

A pipe delivers 9 litres of water in 20 seconds.

(a) Find the amount of water it delivers per minute.

**In 20 seconds, it delivers 9 litres**

**In 60 seconds (i.e. 20 seconds x 3), it delivers (9 litres x 3 =) 27 litres of water per minute**

(b) An empty fish tank is 60 cm long, 45 cm wide and 30 cm high. How long does it take for the pipe to fill the tank completely with water?

**Volume of Tank = 60 x 45 x 30 cm³**

**= 81000 cm³**

**Since 1 litre = 1000 cm³, then 81000 cm³ is equivalent to 81 litres**

**Hence, time taken to fill the tank = 81 litres ÷ 27**

**= 3 minutes**

**Maths@Work**

**No. 8**

A 500-g pack of fertiliser that costs $13 can be applied to 20 m² of lawn.

(a) What is the cost of the fertiliser per kg?

**Since 500g costs $13 and 2x500g makes 1 kg**

**Hence, cost of fertiliser per kg = $26/kg**

(b) Find the mass of the fertiliser that can be applied ot 1 m² of lawn.

**Since 20 m² of land requires 500g,**

**Then 1 m² of land will require (500g ÷ 20 =) 25 g of fertiliser**

(c) A rectangular lawn measures 15 m x 8 m. Find the mass and cost of the fertiliser required for the lawn.

**Area of lawn = 120 m²**

**Mass of fertiliser required = 120 m² x 25**

**= 3000 g = 3 kg**

**Cost of fertiliser = 3 x $26**

**= $78**

**No. 9**

The price of an apartment of area 120 m² is $504 000.

Jenny and her mother shared the cost of such apartment in the ratio of 2:3.

(a) How much did Jenny pay?

**Since Jenny paid 2 out of 5 parts, amount she paid = $504 000/5 x 2**

**= $201 600**

(b) What was the price per m² of the apartment?

**Since 120 m² cost $504 000,**

**Cost of 1 m² = $504 000 ÷ 120**

**= $4200/m²**

**No. 10**

A pure gold cube is of side 3 cm. Its mass is 521.1g

(a) Find the mass of pure gold per cm³.

**Volume of cube = 3 x 3 x 3 cm³ = 27 cm³**

**Mass of pure gold per cm³ = 521.1g ÷ 27 cm³**

**= 19.3 g/cm³**{This is also known as the density, which is the same for all pure elements}

(b) Another gold cube is of side 2 cm. Its mass is 120g.

Is it made of pure gold? Explain briefly.

**Volume of cube = 2 x 2 x 2 cm³ = 8 cm³**

**Density = 120 g ÷ 8 cm³**

**= 15 g/cm³**

**In 1 cm³, we could only find 15g of gold instead of 19.3g.**

**Hence the cube is not made of pure gold.**