Lesson 5 of 14
When a letter stands for a digit
Show on a big screenTwo digits are hidden on a board: A B + 2 8 = 9 1. A digit is one of 0 to 9. A sum where letters hide digits is a cryptarithm.
Type a digit for A and a digit for B. The lab shows the working. Tap Next puzzle for a new board.
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Step 1 of 4
- Each letter hides one digit.
- A B means 10A + B.
- 10A + B = 91 − 28 = 63.
- So A = 6 and B = 3.
The rule
A letter that holds a digit can only be 0 to 9. A letter that starts a number is not 0. If A were 0, A B would only be B.
Rule: A letter is one digit. A B means 10A + B, never A × B.
Write the puzzle as a sum with tens and ones. Work backwards: undo each step with its opposite. Or try digits until both sides match.
Another board: A B × 3 = 96. Here 10A + B is 96 ÷ 3 = 32. So A = 3 and B = 2. Check: 32 × 3 = 96.
Try the lab to finish this lesson.