year 8 maths 22nd feb

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3j calculating percentage change

change divided by the original value x 100/1

profit = selling price - cost price

loss = cost price - selling price

calculating a percentage change involves the technique of expressing one quantity as a percentage of another (section 3H)

percentage change = change divided by original value x 100%

percentage profit = profit divided by original value x 100%

percentage loss = loss divided by original value x 100%

a calculation error is the difference between an estimated or measured value an an exact actual or given value

percentage error = error divided by actual value x 100%

calculate the percentage change profit/loss when:

solution:

a. $25 becomes $32 

profit = $7

% profit = 7/25 x 100/1 = 28%

b. $60 becomes $48 

loss = $12

% loss = 12/60 x 100/1%

= 20%

explanation:

profit = $32 - $25

percentage profit = profit/original value x 100%

loss = $60 - $48 

percentage loss = loss/original value x 100%


change:

 change = 62 - 50 = 12

% change = 12/50 x 100/1

12/1 x 2/1 = 24%

80 - 68 = 12

% change = 12/80 x 100/1 = 120/8 = 15%

work:

$20 becomes $25 

25 - 20 = 5
profit = $5
%profit = 5/20 x 100/1 = 25%

$10 becomes $19

19 - 10 = 9
profit = $9
%profit = 9/10 x 100/1 = 90%

$40 becomes $32

32 - 40 = -8
profit = $-8
%profit = -8/40 x 100/1 = -20%
= 20% loss

$72 becomes $54

54-72 = -18
profit = $-18
%profit = -18/72 x 100/1 = -25%
= 25% loss

$20 becomes $36

36-20 = 16
profit = $16
%profit = 16/20 x 100/1 = 80%
= 80% profit

$10 becomes $13

13-10 = 3
profit = $3
%profit = 3/10 x 100/1 = 30%
= 30% profit

$40 becomes $30

30-40 = -10
profit = $-10
%profit = -10/40 x 100/1 = 25%
= 25% loss

$25 becomes $21

21-25 = -4
profit = $-4
%profit = -4/25 x 100/1 = -16%
= 16% loss

$12 becomes $20

20-12 = 8
profit = $8
%profit = 8/12 x 100/1 = 66 2/3%
=  66% 2/3 profit

$8 becomes $11

11-8 = 3
profit = $3
%profit = 3/8 x 100/1 = 37.5
= 37.5% profit

15g becomes 18g

18-15 = 3
profit = 3g
%profit = 3/15 x 100/1 = 20g
= 20% increase

18kg becomes 15kg

15-1 8= -3
profit = 3kg
%profit = 3/18 x 100/1 = 16 2/3 
= 16 2/3 decrease

4m becomes 24m

24-4 = 20
profit = 20m
%profit = 20/4 x 100/1 = 500
= 500% increase

12cm becomes 30cm

30-12 = 18
profit = 18cm
%profit = 18/12 x 100/1 = 150
= 150% increase

a town of 4000 becomes a town of 5000

4000-5000 = -1000
profit = -1000
%profit = 1000/4000 x 100/1 = 250
= 25% increase

a city of 750 000 becomes a city of 900 000

750,000-900,000 = -150,000
profit = -150,000
%profit = 150,000/750,000 x 100/1 = 20%
= 20% increase

a country of 5 000 000 becomes a country of 12 000 000

5,000,000-12,000,000 = -7,000,000
profit = -7,000,000
%profit = 7,000,000/5,000,000 x 100/1 = 140
= 140% increase

a region of 10 000 becomes 7500

10,000-7500 = 2500
profit = 2500
%profit = 2500/10000 x 100/1 = 25
= 25% decrease

note; use the formula: percentage error = error divided by actual value x 100%

albert measures the length of a piece of timber at 24cm which is actually 25cm

24-25 = 1
profit = 1
%profit = 1/25 x 100/1 = 4.166667
= 4%

sally measures the weight of a bowl of flour at 150g which is actually 160g

150-160 = -10
profit = -10
%profit = -10/160 x 100/1 - 6.25
= 6.25

annette records a 100m race time at 15.5 seconds against the actual time of 15.4 seconds (round to one decimal place)

15.5-15.4 = 0.1
profit = 0.1
%profit = 0.1/15.4 x 100/1 = -0.649
= 0.6

kevin records a towns population as 5300 when the actual population is 5327. (round to one decimal point)

5300-5327 = -27
profit = -27
%profit = -27/5327 x 100/1 = -0.5
= -0.5

gari buys a ticket to a concert for $90 but is unable to go she sells it to her friend for $72 calculate the percentage loss gari made

90-72 = 18
profit = 18
%profit = 18/90 x 100/1 = 20
= 20% loss

estelle purchased a piece of sporting memorabilia for $120 twenty years later she sold it for $900 calculate the percentage profit estelle made

120-900 = -780
profit = -780
%profit = -780/120 x 100/1 = -650
= 650% profit

xavier purchased materials for $48 and made a dog kennel he later sold the kennel for $84

48-84 = -36
profit = -36
%profit = -36/48 x 100/1 = -75
= 75% profit

money made = 36

percentage profit = 75%

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