# Student Thinking #2

Standard

At the beginning of the decimal unit, we included a variety of addition and subtraction problems on the warm-up for practice.

One day we had an addition problem, one that we were using to ensure that students knew how to “carry” when the sum in one column was a double digit number.  The standard way to solve decimal addition is to line up the decimals, then to add from right to left.  “Riley” chose to solve the addition problem a different way.  He split each number into it’s whole number and fraction parts.  He added up the fraction parts first, then added up the whole parts.  Then he added the two results together to get his final answer.

If the problem was 12.37+4.86, he first added together 0.37 and 0.86 to get 1.23.  Then he added together 12+4 to get 16.  Finally he added 16+1.23 to get his final answer of 17.23.

It was a unique way to solve the problem.  It isn’t the most efficient way to solve the problem and it opens up more opportunities for error, but it was fascinating to see how he view the problem and how to solve it.