why questions · Ages 9-12

Why Can a Calculator Be Right and Still Give a Misleading Answer?

A calculator follows the numbers entered, but bad measurements, missing context, or rounded data can make a correct calculation lead to a wrong conclusion.

The whole story

1. At eight on Saturday morning, Maya spread a town map across the library steps. She and Theo had one job before noon: carry six tomato seedlings to the community garden by the pond.

2. The map gave the route lengths in tenths of a kilometer. The Pond Path added to 2.0 kilometers, while Market Lane added to 1.9.

3. Maya checked the addition twice. The calculator returned 1.9 for Market Lane and 2.0 for Pond Path, so she chose Market Lane.

4. Market Lane was only 0.1 kilometer shorter on the map. It was a small difference, but Maya thought every step mattered when six seedlings were waiting in a wooden crate.

5. At the canal, they found the footbridge lifted for a barge. The map had measured distance, but it had not included the bridge schedule.

6. When the bridge finally lowered, they hurried on. The seedlings stayed safe, but the noon bell rang before Maya set the crate inside the garden.

7. After the seedlings were planted, Theo looked back at the map. “Were those route lengths really precise?” he asked. Maya picked up a measuring wheel.

8. Their careful measurements told a different story. Market Lane was 2.04 kilometers, while Pond Path was 1.96, so the route that looked shorter was actually longer.

9. The map’s numbers had been rounded, and the calculator had no way to know about waiting, crowds, or a crate that needed careful carrying. Distance was only one piece of the journey.

10. The calculator had been right all along: it had added the numbers they entered. But bad measurements, missing context, or rounded data can make a correct calculation lead to a wrong conclusion.

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