Two pipes A and B can fill a tank in 10 and 15 hours respectively. If both are opened together, how long will it take to fill the tank?
Options: A: 5 hours, B: 6 hours, C: 8 hours, D: 12 hours
Correct Answer: B
Explanation: Pipe A fills 1/10 per hour, Pipe B fills 1/15 per hour. Combined rate = 1/10 + 1/15 = 5/30 = 1/6. Thus, it takes 6 hours to fill the tank. A common mistake is to average the times (10+15)/2 = 12.5, which is conceptually incorrect for work-rate problems.
If the price of wheat in Punjab increases by 20% and a household wants to keep their expenditure on wheat constant, by what percentage must they reduce their consumption?
Options: A: 15.67%, B: 16.67%, C: 20%, D: 25%
Correct Answer: B
Explanation: To keep expenditure constant when price increases by x%, consumption must be reduced by [x/(100+x)] * 100. Here, 20/120 = 1/6, which is approximately 16.67%. Students often incorrectly choose 20% by assuming a linear relationship, which ignores the base effect of the price increase. In FPSC exams, this 'percentage change' concept is frequently tested in the context of inflation and commodity pricing.
A train 150 meters long is running at a speed of 54 km/hr. How much time will it take to pass a platform 250 meters long?
Options: A: 20 seconds, B: 24 seconds, C: 26.67 seconds, D: 30 seconds
Correct Answer: C
Explanation: Total distance to cover is 150m + 250m = 400m. Convert speed to m/s: 54 * (5/18) = 15 m/s. Time = Distance / Speed = 400 / 15 = 26.67 seconds. A common error is failing to add the train's length to the platform length or failing to convert km/hr to m/s.
What is the value of 0.008 ÷ 0.02?
Options: A: 0.4, B: 0.04, C: 4, D: 0.004
Correct Answer: A
Explanation: To solve, rewrite as 0.008 / 0.02. Multiply both numerator and denominator by 1000 to get 8 / 20, which simplifies to 0.4. Many candidates misplace the decimal point, leading to 0.04 or 4, which are common distractors. Basic arithmetic precision is essential for NTS and PPSC screening tests.
A sum of money doubles itself in 8 years at simple interest. What is the annual rate of interest?
Options: A: 10%, B: 12.5%, C: 15%, D: 8%
Correct Answer: B
Explanation: For simple interest, if the sum doubles, the interest earned equals the principal (P). Using SI = (P*R*T)/100, we get P = (P*R*8)/100. Solving for R gives R = 100/8 = 12.5%. Students often confuse this with compound interest formulas, which would yield a different result.
If 10 workers can build a wall in 15 days, how many days will it take 25 workers to build the same wall?
Options: A: 5 days, B: 6 days, C: 7.5 days, D: 9 days
Correct Answer: B
Explanation: This is an inverse proportion problem: M1*D1 = M2*D2. 10 * 15 = 25 * D2, so 150 = 25 * D2, meaning D2 = 6 days. A common mistake is to treat it as a direct proportion, leading to an incorrect answer of 37.5 days. Always check if more workers should logically take less time.
The average age of 5 members of a family is 24 years. If the age of the youngest member (aged 8) is excluded, what is the new average age of the remaining members?
Options: A: 28 years, B: 26 years, C: 24 years, D: 20 years
Correct Answer: A
Explanation: Total age of 5 members = 5 * 24 = 120 years. After removing the 8-year-old, the total age is 120 - 8 = 112 years. The new average = 112 / 4 = 28 years. Candidates often forget to divide by the new count (4) instead of the original count (5).
A shopkeeper marks his goods 40% above the cost price and allows a discount of 10%. What is his net profit percentage?
Options: A: 30%, B: 26%, C: 34%, D: 24%
Correct Answer: B
Explanation: Let CP = 100. Marked Price = 140. Discount of 10% on 140 is 14. Selling Price = 140 - 14 = 126. Profit = 126 - 100 = 26%. A common trap is simply subtracting 10 from 40 to get 30%, which ignores that the discount is calculated on the marked price, not the cost price.
In a class of 60 students, the ratio of boys to girls is 3:2. How many more girls must be admitted to make the ratio 1:1?
Options: A: 10, B: 12, C: 15, D: 20
Correct Answer: B
Explanation: Initial boys = (3/5)*60 = 36; girls = (2/5)*60 = 24. To make the ratio 1:1, the number of girls must equal the number of boys (36). Therefore, 36 - 24 = 12 more girls are needed. Students often mistakenly try to change the number of boys, which is not allowed by the question.
What is the next number in the series: 2, 6, 12, 20, 30, ...?
Options: A: 36, B: 40, C: 42, D: 44
Correct Answer: C
Explanation: The pattern is based on adding consecutive even numbers: 2+4=6, 6+6=12, 12+8=20, 20+10=30, 30+12=42. Alternatively, it follows the n^2 + n formula (1^2+1, 2^2+2, etc.). This type of logical reasoning is a staple in CSS General Ability papers.