Percentages

Question 1

How do you calculate simple interest?

Answer 1

Take the percentage and convert to a decimal
Multiply the decimal to the number
For multiple years multiply the previous number by the number of years

Question 2

What is the formula for simple interest (if asked for overall total)?

Answer 2

(P×T×R)/100
Where
P = Principal (in £s)
T = Time (in years)
R = Interest rate (%p.a.)

Question 3

Whzt is the formula for compound interest (if asked for overall total)?

Answer 3

P×(1+R/100)^t

P = Principal (original amount)
R = compound interest rate (%)
T = time (years)

Question 4

What is the formula for percentage increase?

Answer 4

(actual increase/original value)*100

Question 5

What is the formula for percentage decrease?

Answer 5

(actual decrease/original value)*100

Question 6

A laptop that normally costs £550 is reduced to £484 in a sale. What is the % reduction in the price?

Answer 6

12%

Question 7

How do you find the original price of an item before a a sale?

Answer 7

100% - Percentage for sale:Price with sale in comparison to original amount
Make the percentage side of the ratio 100 and multiply the right hand side by the same amount

Question 8

What shortcut can be taken when doing repeated percentage change?

Answer 8

Multiply the decimal multiplyers together

Question 9

What is the formula for percentage error?

Answer 9

(approx. - exact)/exact * 100

Question 10

I estimated 260 people in a school concert, but 325 came. What was my percentage error?

Answer 10

20%

Question 11

How do you convert percentages to decimals?

Answer 11

Divide the percentage by 100

Question 12

How do you convert decimals to percentages?

Answer 12

Multiply the percentage by 100