Numerical Ability MCQs: Practice Questions & Shortcut Tricks

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Numerical Ability MCQs: Practice Questions & Shortcut Tricks

Tips & Tricks Concepts

Multiplication by 11: For a 2-digit number ab, the result is a | a+b | b.

Finding Squares (Ending in 5): The square of n5 is n*(n+1) followed by 25.

Unit Digit Method: To check a multiplication, just multiply the last digits of the numbers.

Approximation: If options are far apart, round off numbers before calculating.

Interchangeability: x% of y is the same as y% of x.

Fraction Conversion: Memorize fraction-to-percentage values (e.g., 1/8 = 12.5%) for fast calculation.

Successive Change: For two successive percentage increases x and y, the net increase is (x + y + (xy/100))%.

Successive Discounts: For two successive discounts x% and y%, the net discount is (x + y - (xy/100))%.

False Weights: Profit % = ((True Value - False Value) / False Value) × 100.

Combining Ratios: If A:B = m:n and B:C = p:q, then A:B:C = mp : np : nq.

Relative Speed (Opposite): When objects move in opposite directions, their speeds add up.

Relative Speed (Same): When objects move in the same direction, their speeds are subtracted.

Average Speed (Two Equal Distances): Average Speed = (2 * s1 * s2) / (s1 + s2).

LCM Method: Assume total work = LCM of the individual days to avoid fractions.

Efficiency Concept: Work = Time × Efficiency.

CI Rule of 72: The years it takes for money to double is approximately 72 / (interest rate).

CI vs SI (2 Years): The difference between CI and SI for 2 years is P(R/100)².

Observation over Calculation: Scan the graph/table for the answer before doing any complex math.

Fibonacci Sequence: A sequence where each number is the sum of the two preceding ones, starting from 0 and 1. Example: 0, 1, 1, 2, 3, 5, 8, 13...

Fundamental Logarithm Rules 📜

The Product Rule: logb(MN) = logb(M) + logb(N). Use this to combine separate log terms into one or to break a complex log down.

The Quotient Rule: logb(M/N) = logb(M) - logb(N). Simplifies expressions involving division inside a logarithm.

The Power Rule: logb(Mk) = k ⋅ logb(M). This is the most useful rule for solving equations as it helps bring down exponents.


Change of Base & Key Identities

Change of Base Formula: logb(M) = logc(M) / logc(b). Essential when you need to simplify an expression with multiple bases.

Log of 1: logb(1) = 0. The logarithm of 1 to any base is always 0.

Log of the Base: logb(b) = 1. The logarithm of a number to the same base is always 1.


Core Concepts for Solving MCQs

The Log-to-Exponential Relationship 🔄: logb(x) = y is the same as by = x. If you're stuck on a log equation, immediately rewrite it in its exponential form.

Equating Logarithms: If logb(M) = logb(N), then M = N. Use the other rules to get a single log on each side, then drop the logs and solve.

The Multiplication Principle (The Slot Method) 🎰

Concept: If a task has multiple steps, the total number of ways to complete it is the product of the ways to do each step. Think of filling slots (_ _ _) and multiplying the options for each slot.


Basic Permutation Formula (Order Matters!)

Rule: The number of ways to arrange r items from a set of n distinct items is P(n, r) = n! / (n-r)!

MCQ Tip: Look for keywords like "arrange," "order," "rank," or specific roles (e.g., President, VP). If order is important, it's a permutation.


Permutations with Repetition (Non-Distinct Items)

Rule: The number of distinct arrangements of n items with repetitions is n! / (r1! ⋅ r2! ...), where r is the count of each repeated item.

MCQ Tip: This is most common for arranging letters in a word with repeated letters, like "MISSISSIPPI."


Circular Permutations 🔄

Rule: The number of ways to arrange n distinct items in a circle is (n-1)!

MCQ Tip: Use for seating arrangements around a table. If items can be flipped (like a necklace), divide by 2.


Strategic Tips for Solving MCQs

Identify Keywords: "Arrange/order" points to permutations. "Choose/select" often points to combinations.

Use Casework: For problems with multiple conditions (e.g., "starts with a vowel"), break the problem into smaller cases, solve each, and add the results.

The Complement Rule (The "Not" Rule): Sometimes it's easier to find the total arrangements and subtract the ones you don't want. Useful for questions with phrases like "at least one" or "never together."

Test Your Knowledge

1. The Fibonacci sequence is the sequence of integers: [ ISRO CSE 2007 ]

2. The exponent of 11 in the prime factorization of 300! is: [ GATE IT 2008 ]

3. 25 persons are in a room. 15 of them play hockey, 17 of them play football and 10 of them play both hockey and football. Then the number of persons playing neither hockey nor football is: [ GATE CSE 2010 ]

4. If log(P) = (1/2)log(Q) = (1/3)log(R), then which of the following options is TRUE?

5. Given the digits 2, 2, 3, 3, 3, 4, 4, 4, 4, how many distinct 4-digit numbers greater than 3000 can be formed? [ GATE CSE 2010 ]

6. 5 skilled workers can build a wall in 20 days; 8 semi-skilled workers can build a wall in 25 days; 10 unskilled workers can build a wall in 30 days. If a team has 2 skilled, 6 semi-skilled and 5 unskilled workers, how long will it take to build the wall? [ GATE CSE 2010 ]< /p>

7. Hari(H), Gita(G), Irfan(I) and Saira(S) are siblings. All were born on 1st January. The age difference between any two successive siblings is less than three years. Given the following facts:

i. Hari's age + Gita's age > Irfan's age + Saira's age
ii. The age difference between Gita and Saira is one year. However, Gita is not the oldest and Saira is not the youngest.
iii. There are no twins.

In what order they were born (oldest first)? [ GATE CSE 2010 ]

8. If 137 + 276 = 435, how much is 731 + 672? [ GATE CSE 2010 ]

9. The cost function for a product in a firm is given by 5q2, where q is the amount of production. The firm can sell the product at a market price of Rs. 50 per unit. The number of units to be produced by the firm such that the profit is maximized is: [ GATE CSE 2012 ]

10. A container originally contains 10 litres of pure spirit. From this container, 1 litre of spirit is replaced with 1 litre of water. Subsequently, 1 litre of the mixture is again replaced with 1 litre of water and this process is repeated one more time. How much spirit is now left in the container? [ GATE CSE 2011 ]

11. A transporter receives the same number of orders each day. Currently, he has some pending orders (backlog) to be shipped. If he uses 7 trucks, then at the end of the 4th day he can clear all the orders. Alternatively, if he uses only 3 trucks, then all the orders are cleared at the end of the 10th day. What is the minimum number of trucks required so that there will be no pending order at the end of the 5th day? [ GATE CSE 2011 ]

12. The variable cost (V) of manufacturing a product varies according to the equation V = 4q, where q is the quantity produced. The fixed cost (F) of production of the same product reduces with q according to the equation F = 100/q. How many units should be produced to minimize the total cost (V+F)? [ GATE CSE 2011 ]

13. P, Q, R and S are four types of dangerous microbes recently found in a human habitat. The area of each circle with its diameter printed in brackets represents the growth of a single microbe surviving the human immunity system within 24 hours of entering the body. The danger to human beings varies proportionately with the toxicity, potency and growth attributed to a microbe shown in the figure below:

Microbe Data Figure

A pharmaceutical company is contemplating the development of a vaccine against the most dangerous microbe. Which microbe should the company target in its first attempt? [ GATE CSE 2011 ]

14. What will be the maximum sum of 44, 42, 40, ... ? [ GATE CSE 2013 ]

15. Given the sequence of terms, AD CG FK JP, the next term is: [ GATE CSE 2012 ]

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