# Maths - averages, percentages & product of primes

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- Created by: Serendipitous_dreamer42633
- Created on: 06-03-16 16:03

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- Averages, Percentages, Product of primes.
- Averages
- Add up all of the numbers, then divide by how many there are.
- E.g: 6,7,11 Add the numbers: 6+11+7 = 24 Divide by how many number there are: 24 / 3 = 8 The mean is 8.

- E.g: 42,106,89+1 Add the numbers: 42+106+89+1 = 238 Divide by how many numbers there are: 234 / 4 = 59.5

- Add up all of the numbers, then divide by how many there are.
- Percentages
- Percent means 'out of 100'. E.g: 1/100
- E.g: Calculate 25% of 80. 25% = 25/100. And 25/100 x 100 = 20. So 25% of 80 is 20.
- Reverse percentages
- E.g: In a sale, everything has been reduced by 20%. Kate buys a top for £64. How much was it before it was reduced?
- Workings out: 100-20 = 80. 64 / 0.8 = £80

- E.g: In a sale, everything has been reduced by 20%. Kate buys a top for £64. How much was it before it was reduced?
- E.g: 'l' is 30% of 'k'. 'k' is 90% of 'a'. What percentage of 'a' is 'l'?
- Workings out: 'l' = 30/100 x 'k'. 'k' = 90/100 x 'a'.

- Product of primes
- E.g: Express 72 as a product of primes.
- 72
- 36
- 6 6
- 3 2
- 3 2

- 6 6
- 2

- 36
- 3x3x2x2x2
- 2 (little 3) x 3 (little 2)

- 72

- E.g: Express 72 as a product of primes.

- Averages

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