1TTO §7.1 From description to formula

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§7.1 From description to formula

First there comes an example.

See next slide, showing an exciting nature event.

a. We read this text together.

b. Answer the question below in the next slide.

Roughly how far away is the thunderstorm?

1. 2 km
2. 2 + 2/3 km
3. 2.5 km
4. 3 km

Solution:

It takes the thunder 3 seconds to travel 1 km.

So if you hear the thunder after 8 seconds, then it is

8 : 3 = 2  2/3 km away.

However, because the question said 'roughly' (ongeveer) also

2.5 km is a good answer.

A rule in words about this is:

If you divide the time in seconds the thunder takes to reach you by 3, you get the distance in km.

This Rule in Words is changed into a Formula now:

If you divide the time in seconds the thunder takes to reach you by 3, you get the distance in km. (=Rule in Words)

time in seconds : 3 = distance in km (= Formula)

What does a Formula have, but a Rule in Words does not?

Solution:

A Formula has arithmetic symbols like:

+           -              x      and      :  

(What is Described(=beschreven) only in a Rule in Words, is made into a Calculation in a Formula.)

Let's make a Formula now!

In the next exercise you get some information.

You are asked 

A) to make a Formula and then 

B) to make a Calculation with it.

Formula .... ?

The correct Formula is:

number of balls x 60 + 250 = weight,  or

250 + number of balls x 60 = weight,  or 

weight = number of balls x 60 + 250

So you see that there are more ways to write it down!

Now answer this one, using the Formula you just made!

Calculate the weight of a box containing 6 balls.
The Formula is:
number of balls x 60 + 250 = weight

1. 600
2. 590
3. 580
4. 610

Solution:

Summarising:

Sometimes you have a Description or a Formula in Words.

You can change this into a Formula.

In a Formula you can fill in a given number, to get an outcome.

Like we just did.

Homework time

Time to do 0f §7.1 now: 6, 7 and 8.

Don't forget to 

+ check with the Solutionsbook