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Random Math Tricks for CETS
[thread]
[thread]
MULTIPLYING BY 5
212 multiplied by 5
Approach: divide by 2 and add a zero at the end
212/2=106
Add 0
1060
212 x 5 = 1060
212 multiplied by 5
Approach: divide by 2 and add a zero at the end
212/2=106
Add 0
1060
212 x 5 = 1060
COWS AND CHICKENS PROBLEM
In a farm there are 226 legs and 65 heads. How many cows, how many chickens?
Approach: (Legs/2) - Heads = # of 4 legged animal
(226/2) - 65 = 48 cows
65 - 48 = 17 chickens
In a farm there are 226 legs and 65 heads. How many cows, how many chickens?
Approach: (Legs/2) - Heads = # of 4 legged animal
(226/2) - 65 = 48 cows
65 - 48 = 17 chickens
Permutation
5P2
10P3
7P4
nPr
Approach: n x (n-1) Ă— (n-2).... r times
5P2 = 5x4 =20
10P3 = 10x9x8 =720
7P4 = 7x6x5x4 =840
5P2
10P3
7P4
nPr
Approach: n x (n-1) Ă— (n-2).... r times
5P2 = 5x4 =20
10P3 = 10x9x8 =720
7P4 = 7x6x5x4 =840
Combination
10C2
7C3
5C1
nCr
Apprach: nPr/r! (refer to permutation trick)
10C2= (10x9) /(1 x 2) = 45
7C3 = (7x6x5)/(1x2x3) = 35
5C1 = 5/1 = 5
10C2
7C3
5C1
nCr
Apprach: nPr/r! (refer to permutation trick)
10C2= (10x9) /(1 x 2) = 45
7C3 = (7x6x5)/(1x2x3) = 35
5C1 = 5/1 = 5
MENTAL PERCENTAGE CALCULATION
4% of 75
18% of 50
10% of 100
Approach: if its hard to calculate, just invert it
4% of 75 is hard so lets invert it
75% of 4 = 3
18% of 50 is hard so inverting it
50% of 18 = 9
10% of 100 if this is hard for you then invert it XD
100% of 10= 10
4% of 75
18% of 50
10% of 100
Approach: if its hard to calculate, just invert it
4% of 75 is hard so lets invert it
75% of 4 = 3
18% of 50 is hard so inverting it
50% of 18 = 9
10% of 100 if this is hard for you then invert it XD
100% of 10= 10
Sin and Cos of Special Angles
Cosine is reverse
Cosine is reverse
CONVERTING TEMPERATURES
Celsius to Fahrenheit (roughly)
Multiply by 2 and add 30
Fahrenheit to Celsius(roughly)
Subtract 30 and divide by 2
Note: just look for the nearest answer in the choices
Celsius to Fahrenheit (roughly)
Multiply by 2 and add 30
Fahrenheit to Celsius(roughly)
Subtract 30 and divide by 2
Note: just look for the nearest answer in the choices
DIVISIBILITY RULES
POWER RULES
must memorize, very essential
must memorize, very essential
WORK RATE PROBLEMS
Suppose Person A can do JOB X for 3 hours and Person B for 5 hours. How long will it take if they work together?
Approach: Assume 1 hour of work and calculate their rate together
if A can do 1 whole job in 3 hours, then for 1 hour, he can do 1/3 of JOB X
Suppose Person A can do JOB X for 3 hours and Person B for 5 hours. How long will it take if they work together?
Approach: Assume 1 hour of work and calculate their rate together
if A can do 1 whole job in 3 hours, then for 1 hour, he can do 1/3 of JOB X
if B can do 1 whole job in 5 hours, then for 1 hour he can only do 1/5 of the job.
Together, they can work (1/3+1/5) of the job in 1 hour.
To calculate the time it would take:
t(1/3+1/5) = 1 whole job
t = 1/(1/3+1/5)
t= 15/8 hours
t(1/A+1/B) = 1
t=time
A,B=rate in 1 hr
Together, they can work (1/3+1/5) of the job in 1 hour.
To calculate the time it would take:
t(1/3+1/5) = 1 whole job
t = 1/(1/3+1/5)
t= 15/8 hours
t(1/A+1/B) = 1
t=time
A,B=rate in 1 hr
WHICH IS LARGER
2^300 or 3^200
Approach: Power rule, factor out the exponent
(2^3)^100 or (3^2)^100
(8)^100 or (9)^100
now it is obvious that 9^100 is greater than 8^100 therefore 3^200 is the bigger number
2^300 or 3^200
Approach: Power rule, factor out the exponent
(2^3)^100 or (3^2)^100
(8)^100 or (9)^100
now it is obvious that 9^100 is greater than 8^100 therefore 3^200 is the bigger number
System of Equations
this is my preference but i suggest learning Gauss Jordan Elimination for faster solution of complex systems
I highly recommend BlackPenRedPen for tutorials with this
this is my preference but i suggest learning Gauss Jordan Elimination for faster solution of complex systems
I highly recommend BlackPenRedPen for tutorials with this
BALANCING AVERAGE
Suppose you have a set of { 14, 12,10,x}, determine x to make the average equal to 10
Approach: Balancing
14 - 10= 4
12 - 10= 2
10 - 10= 0
Therefore x should be equal to 4+2+0=6
10-6=4 kulang para maging 10
Suppose you have a set of { 14, 12,10,x}, determine x to make the average equal to 10
Approach: Balancing
14 - 10= 4
12 - 10= 2
10 - 10= 0
Therefore x should be equal to 4+2+0=6
10-6=4 kulang para maging 10
Disclaimer: These are basic skills/concepts you need to know or master. The Cets are much more harder and not so direct. Study hard!
