Average speed: the SAT math trap

Short answer: Average speed = total distance ÷ total time. Never average the two speeds.

The trap, in one question

Tempting answer: 50 mph  (average of 60 and 40)

Correct answer: 48 mph  (240 mi ÷ 5 hr)

Watch it in under a minute

How to spot it in 3 seconds

Average speed = total distance ÷ total time. Never average the two speeds.

FAQ

What is the average speed trap on the SAT?

Example: You drive 120 miles at 60 mph, then 120 miles back at 40 mph. What is your average speed? The tempting answer is 50 mph (average of 60 and 40); the correct answer is 48 mph (240 mi ÷ 5 hr).

How do you avoid the average speed trap?

Average speed = total distance ÷ total time. Never average the two speeds.

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