Percentages from first principles (Year 8)

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“We have surveyed one hundred people and asked them the question….” I’m guessing all of you have watched Family Feud at least once and heard Grant Denyer read out all sorts of questions and received some surprising answers from the players. This game is based on percentages, which is our topic of study for the next week. There are a series of concepts you need to understand, with increasing levels of difficulty, listed below:

•  I understand that percentage means “out of one hundred”. 30% means 30 out of every 100 or 3 out of every 10 or 0.3 out of 1.0
• I can (always, usually, sometimes, never) convert between percentages, fractions and decimals. For example, 25% = 25/100 = 1/4 = 0.25
• I can (always, usually, sometimes, never) calculate the percentage of an amount (with/without) using a calculator. For example, 15% 0f 300 = 15 x 3 = 45
• I can (always, usually, sometimes, never) calculate a percentage discount, profit or loss. For example, a pair of \$80 jeans were on sale with a 10% discount, what is the sale price? \$80 – (10% of 80) = \$80 – \$8 = \$72.00
• I can (always, usually, sometimes, never) work out the percentage increase or decrease of two amounts. For example, the median house price rose from \$150,000 to \$175,000, so the percentage increase was (175,000 – 150,000)/150,000 = (about) 17%

Some resources:

Percentages, Profit and Loss (Year 8)

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Learning Intentions: Solve problems involving profit and loss, and the use of percentages, including percentage increases and decreases, with and without digital technologies.

Whenever you buy something, the shop owner has to put a price on that item, usually so that he can make a profit. Food such as fruit and vegetables will usually have a smaller margin (percentage profit) than more expensive items such as clothing and appliances. In Australia, the “Goods and Services Tax” (GST) of 10% is applied to almost all consumer items, except fresh produce. So, if you pay \$55.00 for an item, \$50.00 is for the shopkeeper and \$5.00 is the GST, which goes to the federal government tax office.