Why 5 + 5 + 5 Doesn't Always Equal 15

Working out the answer to 5x3 may seem simple enough but the solution one student gave has sparked an online debate.

The maths question, which asks pupils to work out 5x3 using the repeated addition strategy, was posted on Reddit.

It shows a Year 3 pupil being marked down for the solution 5+5+5, with the teacher noting the correct working out should be shown as 3+3+3+3+3.

A second question asks students to draw an array to show and solve 4x6, with the student drawing six rows of four as the answer. This is also marked as incorrect, with the teacher highlighting four rows of six as how it should be written out.

The National Council of Teachers of Mathematics (NCTM) in the US defended how the paper was marked, saying it gives students a better understanding of the problems they are solving.

"Part of what we are trying to teach children is to become problem solvers and thinkers," said Diane Briars, president of the NCTM.

"We want students to understand what they're doing, not just get the right answer."

The Common Core State Standards for English and Maths has been widely adopted in the US and outlines what each student should know in each subject by the end of each grade.

Critics claim the different approach can be too confusing for children, while supporters believe the methodology pays dividends when students move on to tackle more difficult problems.

"I would totally argue with the teacher over that for my child," commented one user.

However another replied: "This is a mark of a good teacher. If your question doesn't achieve the desired result then the question was the problem, not the answer."

- NZ Herald