MENTAL MATH
15% of 200
30
Name the solid with 6 faces.
Cube/Cuboid
I have a rule that connects three sides of a right-angled triangle. Without me, you can’t find the hypotenuse. Who am I?
Pythagoras theorem
sin 2θ
2 sinθ cosθ
Equation of a line parallel to x-axis?
y=c
Factorial of 5
120
How many zeroes in a million?
6
I let you replace repeated multiplication with a tidy set of coefficients. Who am I? [(a+b)n]
Binomial Theorem
(a+b+c)2
a2 + b2 + c2 + 2(ab+bc+ca)
A coin is tossed three times. Find the probability of getting exactly 2 heads.
3/8
Square root of 1225
35
What is the sum of the interior angles of a hexagon?
720
I connect the middles of two sides of a triangle,
And I promise something neat and stable:
I run parallel to the base you see,
And half its length I’ll always be.
Who am I?
Midpoint Theorem
Volume of Sphere
V = 4/3 π r³
nCr = ?
n! / (r! * (n – r)!)
49 X 11
539
Complete the series-
2, 3, 5, 9, 17, _
33
I shrink or stretch a triangle, keeping angles true,
Corresponding sides grow or shrink in ratio too.
Shape stays the same, size may vary,
Which theorem am I?
Similarity Theorem of triangles
Sum of an A.P.
S = n/2 * [2a + (n-1)d]
Find the distance between the points (7, −3) and (−1, 5).
√128 or 8√2
If the shopkeeper gives a 20% discount on Rs. 250, what is the selling price?
Rs. 200
A 3-digit number whose tens digit is 5 more than the ones digit. Its hundreds digit is 8 less than the tens digit. What number is it?
194
I live in a circle, my four corners touch,
Opposite angles sum up nicely — that’s my crutch.
I bend and curve but my secret is true,
Add my opposite angles, they’ll make 180° for you.
Who am I?
Cyclic Quadrilateral Theorem
P(A∪B)
P(A) + P(B) − P(A∩B)
The mean of 100 observations is 40. Later it was discovered that two observations, 30 and 50, were wrongly recorded as 20 and 60. Find the correct mean.
Mean = 40 (no change)