These examples gives the idea, how to solve the change in calculations including percentages. The formula used is exactly the same as in previous topic but [i]a[/i], [i]b[/i] and/or [i]p[/i] may need some calculations before the value is known.

[br]Original price of a product is 380 euros. If it is raised by 15 %, what is the new price? [br][br]The original value [i]a[/i] = 380 euros, [i]p[/i] = 0.15  and [i]b[/i] needs to be solved. [br][br][math]\Large b=pa=0.15\cdot 380\text{ euros}=57\text{ euros}.[/math][br][br]The new price will be the original price plus the raise, so the new price is 380 euros + 57 euros = 437 euros. [br]

The value of a share decreased from 20 euros to 5 euros. How much is it in percentages?[br][br][u]Method 1:[/u][br][br]The difference in value is 20 euros - 5 euros = 15 euros.[br][br]Now, [i]b[/i] = 15 euros and [i]a = [/i]20 euros. Thus[br][br][math]\Large p=\frac{15\text{ euros}}{20\text{ euros}}=75\%[/math][br][br][u]Method 2:[br][br][/u]One way of solving this, is to solve how many per cents the new value is from the original  and check how much does it deviate from 100%.[br][br][math]\Large \frac{5\text{ euros}}{20\text{ euros}}-1=-0.75=-75\%[/math].[br][br]The minus-sign tells us, that the value decreased. Thus, the value of the share decreased by 75%.[br]

The cost of cleaning changed from 150 euros to 225 euros. How much is the changes in per cents?[br][br]The basic value is the original value before the change. [br][br][u]Method 1:[br][br][/u]The difference is 225 euros - 150 euros = 75 euros.[br][br][math]\Large p=\frac{75 \text{ euros}}{150\text{ euros}}=50\%[/math].[br][br][u]Method 2:[br][br][/u] [math]\Large p=\frac{225 \text{ euros}}{150\text{ euros}}-1= 0.50=50\%.[/math]