Mental math Flashcards
sq rt sign with 4 next to it
rt(4)
4^(1/4) = 2^(2*1/4) = 2^ (1/2) ~1.4
If you have to add a bunch of #s like 1+2^2+3^2…9^2, trick
first look at answers and see if unit digit is different, if so, just add up the units
16^2
256
Trick to divide by 5
Multiply by 10, divide by 2
Memorize sq rt 5
2.25
5/8
.625
5/6
.833
7/8
.875
.9*2 =
FIRST CHANGE TO FRACTION
9/10*2=1.8
Or think it’s almost 2 but not quite so 1.something
Faster calc with odd percent like 7%
Do 10%/2 to get 5%
Then 1%+1%
15*6
90
235-125 = (do this on paper)
110
Subtracting 3-4
-1
-10 * 10^2
- 10*3, preserve the negative
n^n ends in 1 option
1, 5, or 6
n^n ends in only 2 options
4 or 9
Careless 19+7
26
Careless 9 and a in a problem
A (cap) and straight 9, be careful
33^43 ends in what digit. TRICK
Divide by 4, not 3
Which fractions let you multiply the 1/x to subsequent fractions?
1/9 –> try 5/9=.115
1/11 –> try 5/11=/095
1/6 –> try 5/6 = .167*5=.833
1/7 –> try 5/7 = .14 *5=.7
number divis by 8 if
last 3 digits are
or if you can divide by 2 3 times
number divis by 9 if
sum of digits divis by 9, just like 3
97/7=
NOT 13!!! IT’S 13.SOMETHING
4!
24
2 stems looks similar
2 stems look identical
A or B bc likely a trick that your’e not seeing
D or E
when you have multiple calculations ex: 3x2x2, avoid careless
do each one separately
3x2 = 6
6x2 = 12
careless in division - better to write it out
ex: 78/3
78 / 3 (actually cross out so you don’t put 29 instead of 26)
10% of 10,000
1% of 10,000
Remove one 0 so 1,000
Remove 2 0’s so 100
