Session 4 –Percentages and Money (calculator)

Adding and Subtracting Fractions  Fractions mush have the same denominator in order to add or subtract them.  To do this we must find a common denominator  Change the fractions to equivalent fractions with the same denominator  Add or Subtract the numerators, keeping the denominators the same.

Multiplying Fractions  Multiply the numerators  Multiply the denominators  Simplify the fraction  Exercise 2.6 Question 2  Extension Question 5

Dividing Fractions  Turn the fraction on the right of the divide sign upside down  Change the divide sign to a multiply and complete the question as you would with multiplication  Exercise 2.7 Q1 a,b,c Q3 a,b,c  then Q6,Q7,Q8

Fractions on a calculator  Fractions button, mixed number button  Fractions to decimals  Top number divided by the bottom number

Percentage  Percent = out of 100  A decimal changes to a percentage when multiplied by 100  A percentage is a fraction out of 100  Fractions can be changed to percentages by multiplying by 100

One number as a percentage of another  Write the numbers as a fraction and then…  multiply by 100  or change the bottom of the fraction to 100.  Exercise 4.1 – Q1e to 4e  Then Q7-11

Percentage of a quantity  Divide the quantity by 100, then multiply by the percentage you want.  A useful shortcut may be to find 10%, which can be found by dividing your quantity by 10.

Percentage change  When something is reduced by 20%, you need to find 20% then take tgis away from the original  When something is increased by 50%, you need to find 50% then add it on to the original  Exercise 4.2 Q1-5

Percentage increase and decrease.  A percentage increase measures an increase as a proportion of the original amount. actual increase % increase = x100 initial value Exercise 4.3 Q 2 and 3 (no calc) Q7 and 11

Reverse % problems  If a product is reduced by 20%, and the new value is £10. how much was it before the reduction?  £10 = 80% of the original price  10 / 80 = 1% of the original =  S0 100% = x 100 = 12.5  So 100% price = £12.50

Wages and income tax  Overtime at time and a half = x 1.5 of the normal rate  For income tax, remove tax allowance the calculate a % of the rest  Ex 4.5 Q 1-2  Q 5-9

Credit, bills and best value  We need to be able to compare the cose of buying itmes on credit by working with the deposit and the monthly payments  When trying to work ot the best value, we need to work out the price per unit (eg gram or litre) for each of the options. Another way to think o it is, how much am I getting per penny/per pound.  Exercise 4.6 Q2,- 4

V.A.T  Questions involving VAT are the same as any other involving finding % or % increase and decrease  VAT on most good and services is 17.5%  VAT on gas and electricity is 5%  They will give you the % you need to use in the question.  Exercise 4.7 Q 1 and 3

Simple interest  The amount of money, multiplied by the rate of interest, multiplied by the number of years will give you the total amount of interest you gain.  This type of interest you are paid out each year, so the total in your savings always stays the same, and you cash out the value of the interest.

Compound interest  With compound interest, the interest is added to your account and then earns you more interest the following year.  For the non calculator paper, calculate year by year. On the calculator paper, there is a formula you can use.

Compound interest Exercise A selection of questions Homework – Review Exercise 4