Directions: Use the digits 1 to 9, at most one time each, place a digit in each box on the number line to make the number line true. NOTE: number line not drawn to scale

### Hint

Start with one number and build your number line off of that.

Example start in the middle with 39, what numbers could make this a true number line.

Example start in the middle with 39, what numbers could make this a true number line.

### Answer

There are many answers including 17, 39, 42 and 35, 86, 92

Source: Amanda Dey

24,39,156

24, 39, 78

24 39 57

10 30 40

I posed this problem on an assignment for my math for preservice elementary teachers class, and I was surprised at how many missed it. Some would re-use a digit, some used 0, and some wrote a two-digit number in each box.

17 39 42

I’m wondering about whether we should just pay attention to the placement or whether we should also be paying attention to the spacing on the number line. There should not be infinite answers if spacing matters.