Question

the blue dot is at what value on the number line?
9 13 ?

Explanation:

Step1: Find the interval length

Between 9 and 13, there are 2 intervals (since from 9 to next mark, then to 13). So length per interval: $\frac{13 - 9}{2} = 2$.

Step2: Count intervals from 13 to blue dot

From 13, the blue dot is 2 intervals to the right. Each interval is 2, so total from 13: $2\times2 = 4$.

Step3: Calculate blue dot value

Add to 13: $13 + 4 = 17$.

Answer:

17