Open Middle®
Directions: Using the digits 1 to 9, at most one time each, place a digit in each box to make five true number sentences. You may reuse all the digits for each number sentence.
Hint
If you could use any digits you wanted (and not just the digits 1 to 9), how many possible true number sentences could you make? How can you determine if a number sentence is true?
Answer
There are six possible true number sentences. Four of them are equivalent and those are sin(1π/2), sin(2π/4), sin(3π/6), sin(4π/8). The final two are sin(5π/2) and sin(9π/2).
Source: Robert Kaplinsky in Open Middle Math