A boy moving along a circular path of radius $10\mathit{ m}$ completes $3/4^{\mathit{th}}$ of the circle in $10\mathit{ s}$. The magnitude of speed and distance are

 A boy moving along a circular path of radius $10\mathit{ m}$ completes $3/4^{\mathit{th}}$ of the circle in $10\mathit{ s}$. 
The boy's speed is the distance he travels with respect to time. The distance traveled depends on the path followed by him.
$\mathit{Speed}=\frac{\mathit{Distance}}{\mathit{Time}}$
The path followed by him is three-fourths of the circumference of the circular path.
Distance $d=\frac{3}{4}\times 2\mathit{\pi r}$
Here, $r$ is the radius of the circular path
Distance $d=\frac{3}{4}\times 2\pi \left(10m\right)$
$d=47.14\mathit{ m}$
So, the speed can be calculated as
Speed $=\frac{47.14m}{10\mathit{ s}}$ $=4.71\mathit{ m}/s$

The magnitude of speed and distance are $4.71\mathit{ m}/\mathit{s }$and$47.14\mathit{ m}$, respectively.