The methods of reliable problem solving aplied to a mixture problem concerning the number of stamps bought knowing certain facts about the details.

SureMath,
the math software for 21st century problem
solving, was used to solve this problem.

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The givens_based solution

Word problems encountered in early grades can be usually be solved by the givens-based approach.

As grade level advances this is no longer reliable. Problems of any substance require a concept-based (knowledge-based) approach.

The change from givens-based problems solving to concept-based problem solving requires practice. It is much like changing from hunt and peck typing to touch typing. Both changes require considerable effort but the rewards are substantial.

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these problem solutions.