Maths revision: N2: ratio and proportion

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  • Created by: daniella
  • Created on: 31-05-13 20:00

N2.1: proportion problems

directly proportional: something is directly proportional if as one factor goes up as then the other goes up to

inverse proportion: the opposite to direct proportion if you double one factor the other halfs

what is the symbol for directly proportional? 

how can you show that something is proportional with this symbol if its not directly proportional?

you can write other BIDMAS things in eg...

x ∝ 2y

x ∝ y2

THE REST IS SIMPLE- NO MORE RULE: REVISE EXAMPLES?- NOT REALLY NECESSARY 

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N2.2: Percentage problems

What is a decimal equivalent/multiplier?

its a decimal that you would multiply by to find a percentage of a quantity.

How can you find the decimal equivalent/multiplier?

convert the percentage into a decimal. this is the decimal equivalent/multiplier.

THE REST IS SIMPLE: JUST FINDING PERCENTAGES

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N2.3: Reverse percentage problems

1.) find one quantity as a percentage of another

2.)find the original amount before a percentage change

3.) to find the original amount before the percentage change

EASY- NOT A LOT OF REVISION REQUIRED

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N2.4: Repeated proportional change

what does p.a stand for?   per annum

what does annum mean?  year

what is simple interest?

when the interest in pounds is the same amount each year and the percentage was worked out by the original amount in the bank.

how to figure out simple interest:

1.) figure out how much you would have at the end of the year (by doing simple percentage sums)

EXAMPLE: if the interest was 8% then figure out 8% of the original amount in the bank and add this to the amount in the bank originally.

2.) multiply this by the number of years

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N2.4: Repeated proportional change

what is compount interest?  when interest is worked out not from the original amount in the bank, but from the amount put in (possibly at the start of) each year (or any other given time frame - eg. hour, day , month.

how to figure out compount interest:

1.) N= N0 (1 + r/100)n

key:

N = existing amount at this time

N0 = initial amount

r = interest rate in %

n = time

2.) then substitute values in 

3.) make sure everything is in the correct unit (eg. years, % days ect.)

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the test.

THINGS TO REMEMBER FOR THE TEST:

  • if the mark is more than 1 or if there is space SHOW WORKINGS 
  • look for things that will be given to us in the test 
  • bring a calculator, pencil, sharpener, rubber, pen ruler and maths set.
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N2.5: Ratio problems

how to do ratios:

SIMPLE- NO PROPER RULES- GO OVER QUESTIONS

how to do rations with 1:n / x:n/ n:1 / n:x (dont worry about decimals):

SIMPLE- DON'T OVERTHINK

1.) devide the x number by itself to make 1

2.) devide the n number by the first number and this is n

What to remember:

1.) MAKE SURE THAT YOU WRITE THE RATIOS IN THE RIGHT ORDER! if it says cements to sand write the numbers in this order

2.) cancel it down to its simplist form - what do all sides devide into? (highest common factor!)

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N2.5: Ratio problems

How to simplify ratios with a calculator:

1.) use the fractions button

2.) type in the first number in the numerator position and the second in the denominator button.

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N2.5: Ratio problems

what are parts?

how many times something needs to be shared into

How to devide a quantity in a given ratio:

1.) first find the total number of parts or pots  (eg. if the ratio is 3:4 --> 3 + 4 =7)

2.) devide the total number of items by the amount of parts (lets call this answer F)

3.) multiply each ratio section by F (e.g. if F= 100 --> 3x 100 = 300 --> 4 x 100 = 400 --> answer = 300:400

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