Basic Arithmetic MCQs with Step-by-Step Explanations
Q1: If a car travels 150 km in 3 hours, what is its average speed?
\text{Step 1: Formula for average speed: } \text{Speed} = \frac{\text{Distance}}{\text{Time}}
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\text{Step 2: Substitute the given values: } \text{Speed} = \frac{150 \text{ km}}{3 \text{ h}}
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\text{Step 3: Simplify: } \text{Speed} = 50 \text{ km/h}
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Answer: 50 km/h
Explanation: Average speed is calculated as distance divided by time. Here, dividing 150 km by 3 hours gives 50 km/h.
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Q2: The ratio of boys to girls in a class is 3:2. If there are 30 students, how many are boys?
\text{Step 1: Total parts in the ratio} = 3 + 2 = 5
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\text{Step 2: Value of one part} = \frac{\text{Total students}}{\text{Total parts}} = \frac{30}{5} = 6
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\text{Step 3: Number of boys} = 3 \times 6 = 18
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Answer: 18
Explanation: Ratio 3:2 means 3 parts boys and 2 parts girls. Divide total students by total parts to find one part, then multiply by 3 for boys.
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Q3: A price of $500 is increased by 20%. What is the new price?
\text{Step 1: Formula for new price after increase: } \text{New Price} = \text{Original Price} + \frac{\text{Percentage Increase}}{100} \times \text{Original Price}
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\text{Step 2: Substitute values: } 500 + \frac{20}{100} \cdot 500
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\text{Step 3: Calculate: } 500 + 100 = 600
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Answer: 600
Explanation: 20% of 500 is 100. Adding it to the original price gives 600.
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Q4: Find 15% of 240.
\text{Step 1: Formula: Percentage of a number} = \frac{\text{Percentage}}{100} \times \text{Number}
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\text{Step 2: Substitute values: } \frac{15}{100} \cdot 240
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\text{Step 3: Calculate: } 0.15 \cdot 240 = 36
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Answer: 36
Explanation: Convert 15% to decimal 0.15 and multiply by 240 to get 36.
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Q5: If a sum of $1000 is invested at 5% per annum simple interest for 3 years, find the interest.
\text{Step 1: Simple Interest formula: } SI = \frac{P \cdot R \cdot T}{100}
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\text{Step 2: Substitute values: } SI = \frac{1000 \cdot 5 \cdot 3}{100}
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\text{Step 3: Calculate: } SI = \frac{15000}{100} = 150
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Answer: 150
Explanation: Multiply principal × rate × time, then divide by 100. Step by step: 1000 × 5 = 5000, 5000 × 3 = 15000, divide by 100 = 150.