SWC#2 Ratio tables

• Wiskunde
• Middelbare school
• havo, vwo
• Leerjaar 1

1hvt - to do today 

9:40

10:00 

10:30 

11:00 

11:30

11:50

20 mins of introduction of ratio tables

25 minutes of working in silence - zen mode

30 minutes - break

20 mins of working - talking is allowed

final time to hand in readers of Converting Units + C2

analyzing results of the BT C2

scientific calculations week #2

 

RATIO TABLES

GOAL of this lesson: 

YOU KNOW HOW TO CALCULATE IN A RATIO TABLE

Something you measure is called a quantity. 

E.g. mass      

What is the symbol of mass? 

A quantity is measured using a unit.

E.g. gram

What is the symbol of a gram? 

TAKE NOTES! What is a RATIO?

* indicates how big or small a quantity is when compared to another

> 20 cookies fit into 1 package

    the RATIO = 20:1

> you need 200 grams of flour to bake 2 muffins,

    so the RATIO is 200 : 2          or better          100:1

cookies	20	40	80
pack	1	2	4

Why is 100:1 better than 200:2 ?

Both expressions mean the same.

However a RATIO is always written with:

THE SMALLEST POSSIBLE WHOLE NUMBERS ! 

How the calculate in a ratio table?

example 1 

It's about the euros earned by working  a number of hours.

Think about how to get the numbers on the dots.

euros	5	...	...
hour	2	6	36

Calculating with a ratio table - solution

Multiplying HORIZONTALLY is simplest here:

2 x 3 = 6, so for 6 hours worked you get 5 x 3 = 15 euros

6 x 6 = 36, so for 36 hours worked you get 15 x 5 = 90 euros

euros	5	15	90
hour	2	6	36

another practice example...

example 4:

Let's try to find the missing number!

In the next slide I will show you a handy METHOD.

grams	500	240
euros	750	...

STEP 1: calculate the price in euros for just one gram

STEP 2: you can calculate the price of every amount of grams by multiplying by the amount of grams!

grams	500	1	240
euros	750	...	...

Now that we know that 1 gram costs 1,5 cents, we multiply 1,5 by 240!

240 x 1,5 = 240 + 120 = 360 cents.

Write this table in your notebook, and add the correct arrows and calculations to the ratio table. 

grams	500	1	240
euros	750	1.5	360

The reader calls this method:

'Adding a number as an INTERMEDIATE STEP (=tussenstap)'

This intermediate step is mostly the number 1.

However it could also be 10, 50 or any handy number!

It depends on the situation.

grams	500	1	240
euros	750	1.5	360

example 5:

TASK:

Find the easiest way to get the missing numbers.

grams	200	20	220
cents	600	...	...

example 6:

Again find the missing numbers.

grams	40	2	38
cents	160	...	...

example 6:

Solution:

This time SUBTRACTING does the trick!

This is because 40 - 2 = 38

First we calculate that 2 grams cost 8 cents.

Then we do       160 - 8 = 152 cents.

grams	40	2	38
cents	160	8	152

on the back tables 

(the long/empty ones)

EVERYTHING, except a pencil or red/green/purple pen

and your calculator

analyze test

Look at your answers and check if I've checked it correctly.

THERE'S a MiStAkE !                      write it on your post-it!

Look at the types of questions you missed points on.

Count the R / T1 / T2 / I questions and write it down on your post-it.

DONE?