A student wrote these three formulas. Each one has a mistake in the brackets…

Plan. In each line, the division is done before the addition. The brackets that the student wanted are missing.

1. a + b + c / 3 works out c / 3 = 4.0 first, and then 6 + 9 + 4.0 = 19.0. Fix: (a + b + c) / 3 = 27 / 3 = 9.0.
2. a + b / a works out b / a = 1.5 first, and then 6 + 1.5 = 7.5. Fix: (a + b) / a = 15 / 6 = 2.5.
3. a + b / 2 works out 9 / 2 = 4.5 first, and then 6 + 4.5 = 10.5. Fix: (a + b) / 2 = 7.5.