A letter can hold a number
Shake a closed tin. Marbles rattle inside. Three more lie on the table.
Step 1 of 3
- A closed tin. Call the number of marbles inside n.
- Three loose marbles, outside the tin.
- Total = n + 3.
Rule: a letter can hold a number nobody has chosen yet. Such a letter is a letter-number, also called a variable. The number it stands for is its value. n + 3 is an expression. It waits for a value. It turns into a number once n has a value.
Use 5 for n: n + 3 = 5 + 3 = 8. Use 20 for n: n + 3 = 20 + 3 = 23. One line, two answers, because n has no fixed value.
A jar holds m marbles. n and m may hold different numbers. So they need different letters.
Slide n and m. Watch the three lines change.
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