Why does my child think the distance from (1, 2) to (4, 6) is 7?
Your child adds the changes in x and y to find a distance instead of using Pythagoras, such as 7 for (1, 2) to (4, 6).
Why children do it
Adding the distances across and up gives the length of a path along the grid, not the straight line between the points. The straight line is the longest side of a right-angled triangle, so Pythagoras finds it: √(3² + 4²) = 5.
How to help at home
Ask them to draw the right-angled triangle between the points: the distance is its longest side.
The right way
Find the distance between (3, −3) and (19, 9).
- 19 − 3 = 16The change in x.
- 9 − (−3) = 12The change in y.
- √(16² + 12²) = √400Square them, add, and take the square root.
- 20The square root of 400 is 20.
Find out where your child is
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Start the free checkRelated mistakes
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