Back to Quantities — Problem 3 · Task Set 29

HSN.Q Tutor Intake — Units, Quantities, and Accuracy

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Grade 9·13 problems·~15 min·Common Core Math - HS Number and Quantity·domain·q

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Procedures

The formula for distance is $d = r \times t$ , where $r$ is speed
in km/h and $t$ is time. A car travels at $r = 80$ km/h. A student
is given $t = 90$ minutes and computes $d = 80 \times 90 = 7{,}200$ .
What is wrong with this calculation?

The multiplication is wrong; $80 \times 90 = 720$ , not 7,200.

The formula $d = rt$ does not apply to cars.

The units are inconsistent: $t$ must be in hours, not minutes.
The result 7,200 has units of km·min/h, not km.

Nothing is wrong; 7,200 is the correct distance in km.