I developed this calculator to tackle the Make Ten puzzle, a mathematical game commonly played on trains in Sydney, Australia. In this game, passengers use the four-digit number assigned to each train carriage and apply arithmetic operations to achieve the sum of 10. For instance, with the number 1234, one can perform 1 + 2 + 3 + 4 to reach the target.

This posed a mental challenge for me with the numbers 6, 6, 7, and 8. After dedicating two days to it, I successfully achieved the goal of making ten at 2 am. The objective of the challenge was to reach the sum of "10" using the arithmetic operators +, -, *, /, and parentheses ().