#### Answer

$2$ radians

#### Work Step by Step

Step 1: The formula to be used here is $s=r\theta$ where s is the length of the arc intercepted, r is the radius and $\theta$ is the central angle of measure in radians.
Step 2: $s=r\theta$
Step 3: $20=(10)(\theta)$
Step 4: Multiplying both sides by $\frac{1}{10}$,
$20\times\frac{1}{10}=10\times\theta\times\frac{1}{10}$
Step 5: $\frac{20}{10}=\theta$
Step 6: $\theta=2$ radians