Move One Rod
Read the puzzle
Rods form a digital-style equation: 3 - 8 = 7. The 3 uses five rods, the minus sign one, the 8 seven, the equals sign two, and the 7 three (a top rod and two on the right). The equation is false. Lift exactly one rod and place it somewhere else so the equation becomes true. What is the true equation?
Move exactly one rod. What is the true equation?
9 − 8 = 1
The top rod of the 7 turns the 3 into a 9.
How to solve it
Look at what each digit can become with one rod taken away or added.
3 - 8 = 7 is false, since 3 - 8 = -5. The 7 is made of three rods; take away its top rod and it becomes a 1, so the right side becomes 1. Now find a home for that spare rod. A 3 with one extra rod in its upper-left position becomes a 9.
That gives 9 - 8 = 1, and 9 - 8 is indeed 1.
The usual dead end is turning the minus into a plus: that uses the one move but leaves 3 + 8 = 7, which is still false. Quick check: the rod count is the same before and after, 18 in total (5 + 1 + 7 + 2 + 3 before, 6 + 1 + 7 + 2 + 2 after), and only one rod has moved. The true equation is 9 - 8 = 1.
