Change factor (Förändringsfaktor)

Ämne / Topic

Determining the change factor and using change factor to calculate the old or new value.

Inlärningsmål / Learning Goals

Understand the meaning of change factor.

Be able to calculate the old value, the new value or the change factor when given two of the values.

Google Slides & Videos

3. Aktiviteter / Key Activities

Lowering and raising of change factor.

To explore this concept, the teacher will be doing a examples with the class, before giving the learners two examples to complete on their own.

Example 1: (Teacher led example)

An electric bass guitar costs SEK 12 500.

The price is lowered by 30%.

What is the new price?

Step 1: Find the change factor.

Change factor = 100% - 30% (because it is an price reduction, we subtract)

= 70%

= 0,7

Step 2: Find the new price

New value = change factor x old value

= 0,7 x 12 500

= SEK 8 750

What happens if there is a price increase?

The guitars price is increased by 30%

Step 1: Find the change factor.

Change factor = 100% + 30% (because it is a price increase, we add)

= 130%

= 1,3

Step 2: Find the new price.

New value = change factor x old value

= 1,3 x 12 500

= 16 250

Example 2: (Teacher led example)

A microphone cost SEK 1 450.

It goes on sale with a 40% discount. A month later its price is further discounted by 30%.

What is the new price of the microphone?

Method 1: Working with each discount seperatley

Step 1: Find the change factor for the first discount

Change factor = 100% - 40% (because it is an price reduction, we subtract)

= 60%

= 0,6

Step 2: Find the new price after the first discount

New value = change factor x old value

= 0,6 x 1 450

= SEK 870

Step 3: Find the change factor for the second discount

Change factor = 100% - 30% (because it is an price reduction, we subtract)

= 70%

= 0,7

Step 2: Find the new price after the second discount

New value = change factor x old value

= 0,7 x 870

= SEK 609

Method 2: Using both discounts together.

New value = Change factor 1 x change factor 2 x old value

= 0,6 x 0,7 x 1 450

= SEK 609

Example 3: (learners attempt in pairs)

In 2015 a mini submarine dived to the depth of 4 500 m.

In 2018 a mini submarine dived to a depth 45% deeper than in 2015.

What was the new depth?

Change factor = 100% + 45%

= 145%

= 1,45

New value = change factor x old value

= 1,45 x 4 500

= 6 525 m

Example 4: (Learners attempt on their own)

You deposit SEK 10 000 into a savings account. The first year the interest rate is at 3.5%.

The year after that, the interest rate drops to 3 %.

How much money will be in your account after 2 years?

Round off to the nearest crown.

Change factor 1 = 100% + 3,5% Change factor 2 = 100% + 3%

= 103,5% = 103%

= 1,035 = 1,03

New value = Change factor 1 x Change factor 2 x old value

= 1,035 x 1,03 x 10 000

= 10 660,5

= 10 661 kr

4. Kolla vad eleverna kan / Check for understanding / Exit ticket

Learners will answer a question that will be presented to them by the teacher.

The learners will complete the question and hand it to the teacher before they leave.

Three years ago, Mike had 400 people reading his blog per day. In the last three years the readers of his blog per day, increased by 20% per year.

What is the percentage increase of his readers?

5. Stängning / Closure / Summary of lesson

Review how to calculate change factor for percent increase and decrease.