Temperature Changes

A word problem hides a calculation inside a story. At 9 pm the thermometer reads 3 degrees. By 3 am the temperature has fallen 8 degrees. What does it read at 3 am? Falling means taking away, so the story is asking for 3 minus 8.

For a story, the board starts empty and you type every line yourself in the box for new lines, pressing Enter after each one. First pick a letter for the answer, t for temperature. Then write the letter equal to the calculation the story describes: t = 3 - 8. On the next line, work that calculation down to one number: t = -5. When you press Check, the board reads your last line, so it must be the letter equal to a single number.

Why the letter? It says what your number means. A bare -5 could be anything; t = -5 says the temperature is -5 degrees. The first line also keeps a record of how you read the story, so a slip shows up right where it happened. Words become signs: warmer or rises means add, colder or falls means subtract.