Making a 10 in other to solve an addition or subtraction problem involves, thinking of one of the digits as being 10 first, then adding or subtracting the remainder.
- The circled problems involves subtraction of values between digits less than 10, hence, the reason Jan had problems dealing with them.
Taking a look at the values given :
- 14 - 7
- 8 - 2
- 9 - 4
- 15 - 6
- 12 - 8
- The only circled problems are : 8-2 and 9-4
- All the circled problems involves subtraction operation between digits less than 10.
- The fact that the digits are less than 10 could be a possible reason why Jan couldn't make a 10 in other to solve the equation.
- All other problems with values greater than 10 were solvable by Jan by making a 10.
Therefore, we can conclude that the fact that digits in the circled problems are below 10 is the reason why Jan was not able to solve them by making a 10.
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