Everyone knows these problems and answers.
What matters is Fast, (almost)Mental solutions
by Lateral Unconventional methods.

QUESTION 1/20:
The area of the in-circle of an equilateral triangle is 123 units². What is the area of the circum-circle of the same triangle?

QUESTION 2/20: 97² + 103² = ?

QUESTION 3/20:
Prakash walks clockwise along a circular track, 300m long, once every 3 minutes. Ramesh walks anticlockwise once every 4 minutes. What is the time between two consecutive crossings?

QUESTION 4/20:
The ratio of a 2-digit number and the number obtained by reversing the digits is 17 : 5. What is the number?

QUESTION 5/20:
A trader puts the prices up by 25% just 2 months before the festival season. One month before the festivals what exact discount will he offer to realise the original price?

QUESTION 6/20:
While calculating the average of some natural numbers starting from 1, one number was missed and the average worked out to be . What was the missed number and how many numbers were taken?

QUESTION 7/20:
A and B run round a circular track 800m long. A’s speed is 250m per minute ans B’s is 200m per minute. If both run in the same direction, when will they first meet again at the ‘start’?

QUESTION 8/20:
A circle is circumscribed by an equilateral triangle. If the radius is 2cm, what is the area of the triangle?

QUESTION 9/20:
A, B & C together started a work on the 1st of October. A could have done the work alone in (1/11)th of the month. B could have done the work alone in (1/7)th of the month. C could have done the work alone in (1/13)th of the month. When will they finish the work?

QUESTION 10/20:
Express the value correct to 4 d.p. .

QUESTION 11/20:
A lotus flower is one span above the water. Wind starts blowing. As the intensity of wind increases the flower slowly moves and just submerges in the water at a distance of 4 spans from the original position. What is the depth of the water?

QUESTION 12/20: = ?

QUESTION 13/20:
In an A. P., T₃ + T₅ + T₁₀ = T₆ + T₈. If T_n = 0, find n.

QUESTION 14/20:
The cost of two TV’s are in the ratio 13 : 7. The government charged a flat surcharge of Rs.15000 per TV. Now the ratio became 8 : 5. What was the cost of the economical TV before the surcharge?

QUESTION 15/20:
If Rs.8000 is invested at 7.5% p.a. for 2 years, what is the difference in the interests by S.I. and C.I. (compunded annually)?

QUESTION 16/20:
Two cylinderical candles. One is 3cm in diameter and 8.5cm long while the other is 5cm in diameter and 6.25cm long. The first one burns at the rate of 2.25cm per hour and the second one at 1.5 cm per hour. If both are kept side by side on an even surface and lit at the same time. How long after will the flames be at the same level?

QUESTION 17/20: A peacock is perched at the top (P) of a vertical pole 8m tall. It spots a snake (S), 32m from the pole, gliding towards its hole (H) at the foot of the pole. Pouncing obliquely, the peacock picks the snake at (C). If speeds of peacock and snake are equal, how far from the foot of the pole did the peacock pick the snake?

QUESTION 18/20:
A 3m deep pit measuring 56m by 24m is dug in a rectangular field measuring 264m by 56m and the soil is evenly spread on the field. What is the rise in the level of the field?

QUESTION 19/20:
Priya’s maths teacher taught the class how to fill magic squares fast. She drew a Jumbo 25 x 25 square and started to fill the consecutive numbers from 1. What will be the row or column or diagonal total?

QUESTION 20/20:
Anil Amb was going to give Rs.100 to the beggar whom he regularly sees at the trafic signal. The beggar intercepted and said, “Sir, I don’t want this today. But I would like you to give me Re.1 today and on every following day, twice the amount of the preceding day, for just 20 days.” Anil thought this was good fun and readily agreed. How much did he pay in all, in 20 days?