MENTAL MATH
25% of 280
300
I’m a two-digit number that equals 9 times the sum of my digits. What number am I?
81
a/b = c/d implies (a+b)/b = (c+d)/d
NAME THE RULE
COMPONENDO
VOLUME OF A CUBOID
L X B X H
ANGLE IN A SEMI-CIRCLE = ?
90 DEGREES
A NUMBER DOUBLED AND THEN INCREASED BY 15 BECOMES 79. WHAT IS THE ORIGINAL NUMBER?
32
2, 3, 5, 8, 13, ?
21
This theorem states that if a line is drawn parallel to one side of a triangle, it divides the other two sides proportionally.
Basic Proportionality Theorem
FORMULA FOR COMPOUND INTEREST
CI = P (1+ R/100) N
A bag contains 5 red, 3 blue, and 2 green balls.
One ball is drawn at random.
What is the probability that the ball is NOT red?
1/2
5678 + 3496 - 1287
7887
First term of an AP is p and the common difference is q, then it’s 10th term is ?
p+9q
COORDINATES OF THE CENTROID OF A TRIANGLE
A (x1,y1) , B( x2,y2) and C ( x3, y3)
(x1 + x2 + x3) / 3 , (y1 + y2 + y3) / 3
In a right triangle, what is the trigonometric ratio for cos θ?
ADJACENT/HYPOTENUSE
FIND x
x + 3y = 6 and 2x - 3y = 12
6
SQUARE ROOT OF 28561
169
A triangle has sides 7, 9, and 12. Its largest angle is opposite which side?
Opposite side 12.
The angle subtended by an arc at the centre is twice the angle subtended at any point on the remaining part of the circle.
Angle at Centre = 2 × Angle at Circumference Theorem
TOTAL SURFACE AREA OF A HEMISPHERE
3πR2
If a number is increased by 20% and then decreased by 20%, what is the net percent change?
-4% (a 4% decrease).
THE VALUE IS INCREASED BY 35% AND BECOMES 455, WHAT WAS THE INITIAL VALUE?
700
How many times do the clock's hands form a right angle between 3:00 PM and 6:00 PM?
5 TIMES
Once two triangles are proved congruent, this theorem allows you to conclude that all corresponding sides and angles are equal.
CPCT (Corresponding Parts of Congruent Triangles)
MODE = _MEDIAN - _MEAN
3,2
SUM OF FIRST 20 ODD NUMBERS?
400