WAEC 2012 Mathematics · Question 4

Mr. Manu travelled from Accra to Pamfokromb a distance of 720km in 8 hours. What will be his speed in m/s?

Options

A.25m/s
B.150m/s
C.250m/s
D.500m/s

Answer: A. 25m/s

Explanation written with AI and checked against the answer key

Analyze the question: We need the average speed in m/s, given a distance of 720 km covered in 8 hours. Concept: Speed = Distance ÷ Time. The answer must be in metres per second, so convert km to m and hours to seconds. Solution: Step 1: Find the speed in km/h. Speed = 720 km ÷ 8 h = 90 km/h Step 2: Convert km/h to m/s. 1 km = 1000 m and 1 hour = 3600 s, so 90 km/h = 90 × 1000 ÷ 3600 m/s = 90000 ÷ 3600 = 25 m/s Check by converting first: Distance = 720 × 1000 = 720,000 m Time = 8 × 3600 = 28,800 s Speed = 720,000 ÷ 28,800 = 25 m/s ✓ The correct option is A. 25 m/s. Tip: To convert km/h to m/s, multiply by 5/18 (that is, 1000/3600). Here, 90 × 5/18 = 25. To go from m/s to km/h, multiply by 18/5. Also, if an option looks too big, such as 250 m/s for a road journey, it is likely wrong, since 25 m/s is already about 90 km/h, a normal highway speed.

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