Mathematics/General Ability MCQs
Topic Notes: Mathematics/General Ability
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
161
The price of an item was increased by 10%. This new price was then reduced by 10%. If the latest price is Rs 99, what was the original price?
Answer:
100
A 10% increase followed by a 10% decrease results in a net 1% decrease. So, 99% of original price = Rs 99. Original price = 99 / 0.99 = Rs 100.
162
A machine depreciates by 10% per year. Its present value is Rs 8100. What was its value 2 years ago?
Answer:
10000
Let the value 2 years ago be P. P(1 - 10/100)^2 = 8100. P(0.9)^2 = 8100. P * 0.81 = 8100. P = 8100 / 0.81 = 10000.
163
A town's population increases by 5% annually. If the current population is 4000, what will it be in 2 years?
Answer:
4410
Population after 2 years = P(1 + r/100)^2 = 4000(1 + 5/100)^2 = 4000(1.05)^2 = 4000 * 1.1025 = 4410.
164
Successive discounts of 20% and 10% are equivalent to a single discount of?
Answer:
28%
Equivalent discount = A + B - (A*B)/100. So, 20 + 10 - (20*10)/100 = 30 - 2 = 28%.
165
The salary of an employee is first increased by 50% and then decreased by 50%. The net change is:
Answer:
25% decrease
A common percentage increase and decrease of x% results in a net decrease of (x^2)/100 %. Here x = 50. Decrease = 50^2 / 100 = 2500 / 100 = 25% decrease.
166
The tax on a commodity is diminished by 15% and its consumption increases by 10%. The effect on revenue is?
Answer:
6.5% decrease
Revenue = Tax * Consumption. Net effect = -15 + 10 + (-15 * 10)/100 = -5 - 1.5 = -6.5%. The revenue decreases by 6.5%.
167
If the radius of a circle increases by 20%, its area increases by:
Answer:
44%
Area is proportional to the square of the radius. Successive increase of 20% twice: 20 + 20 + (20*20)/100 = 40 + 4 = 44%.
168
The length of a rectangle is increased by 10% and its breadth is decreased by 10%. What is the change in area?
Answer:
1% decrease
Net change = 10 - 10 + (10 * -10) / 100 = 0 - 1 = -1%. A negative sign indicates a 1% decrease in area.
169
A number decreases by 10%, then increases by 20%. What is the net percentage change?
Answer:
8% increase
Using formula A + B + AB/100, where A = -10 and B = 20. Net = -10 + 20 + (-10*20)/100 = 10 - 2 = 8. Since it is positive, it is an 8% increase.
170
A number is increased by 20% and then by 30%. What is the total percentage increase?
Answer:
56%
Use the successive percentage formula: A + B + (A*B)/100. 20 + 30 + (20*30)/100 = 50 + 6 = 56%. Let number be 100 -> 120 -> 156. Increase is 56%.