Proportion and percentage.ppt

Proportion and Percentage Ratio and Proportion Let x be the number of potatoes required to serve 28 people. Cross multiply 4x = 5 (28) 4x = 140 Example 1 A recipe that serves 4 people uses 5 potatoes. How many potatoes are needed to serve 28 people? Since the recipe is the same, we have two equivalent ratios: # of people: # of potatoes: # 1 # 2 # 3 # 4 Divide by 4 to find x x=35 potatoes direct proportion : An increase or decrease in one quantity will lead to an increase or decrease of the other quantity in the same proportion . It takes 6 people 8 days to do a piece of work . How long will it take 12 people to do the same piece of work ,assuming they all work equally hard ? Example 2 THE ANSWER : 4 days Inverse proportion : One quantity increases in the same proportion as the other quantity decrease. Percentage This phrase per cent comes from the Latin ‘per centuri’ which means ‘as per hundred’. A percentage is a ratio in which the second quantity is always 100 A percentage is a fraction in which the denominator is always 100 16 or 16.00 % 1. a. Find 20% of 80. 2. a. What is 35% of 20? 7 or 7.00 3. a. There is a discount of 25% off on a $60 pair of shoes. How much are the shoes? $45 4. a. A shirt cost $30 plus 7% tax. What is the total cost? $32.10 Writing a percentage as a fraction Examples : 1. 5% 2. 250% Profit and loss Loss =cost price – selling price Profit =selling price – cost price Examples: 1. A shopkeeper buys an article for ＄500 and sells it for ＄600 ，what is the percentage profit? Profit =selling price – cost price =＄600-＄500 =＄100 2. A person buys a car for ＄16000 and sells it for ＄12000. calculate the percentage loss . Loss =cost price – selling price =＄16000-＄12000 =＄4000 * *