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Maths Chapter 3- Consumer arithmetics (simple interest (e.g. Gilbert…
Maths Chapter 3- Consumer arithmetics
3A- Percentages
% of an amount
e.g. 23% of $400 = 0.23 x 400
= $92
expressing one quantity as a % of another
1st quantity/ 2nd quantity X 100%
3B- Finding the whole
e.g. if 5% is $6
5% =$6
1% =6/5
=1.20 X 100% =1.20 X 100 =120
$6= 5% of whole OR 6=O.O5 X whole
Commission
commission= % of sale
e.g. Marvin gets 6% commission if he sells $8500, what does he earn?
Commission= 6% of $8500
= 0.06 X 8500
= $510
Profit & loss
e.g. vergil bought a clock for $32 and wants to make a 28% profit what price should he sell the clock for
profit = 28% of $32 = 0.28 X 32
= $8.96
%= 100% + 28%
= 128% SP=128% of 32
= 1.28 X 32
= 40.96
simple interest
I= PRT
I= Interest (money earnt)
P= Principal (amount at beginning)
R= Interest Rate,
AS A DECIMAL
T= Time period in
YEARS
A=P+I
e.g. Gilbert borrows $8000 at 4.2% p.a. SI for 6 years how much does he repay in total
P= $8000 R= 4.2% (0.042) T= 5 years I=PRT I= 8000 X 0.042 X 5
= $1680
A= Final amount (amount at end)
3F- Compound Interest
P= principal/original amount
R= interest Rate (% divided by 100) decimal
T= Time (number of years) compounding annualy
e.g. hildebrand borrows $18000 for a car at 4.6% p.a. for 5 years compounding annualy. how much interest will this loan cost him
P=
$18000
R=
4.6 (0.046)
T=
5 years
A=
P(1+R)t
=
18000 x 1.046 5
=
22538.81
A-P=
22538.81-18000
I=
$4538.81
3G depreciation (loss in value)
appreciation (growth)
A=P(1+R) t
Decpreciation (decay)
A= P(1-R) t