In a 100 m race, A gives a start of 10 m to B but still beats B by 5…

The correct answer is Option (3) → 5.37 km/hr

With a start of 10 m, B runs only 90 m. B's speed in m/s is

    \( \displaystyle 4.5\times\frac{5}{18}=1.25\ \text{m/s} \)

so B takes

    \( \displaystyle \frac{90}{1.25}=72\ \text{s} \)

A finishes 5 s earlier, so A runs 100 m in 72 − 5 = 67 s:

    \( \displaystyle \text{Speed of A}=\frac{100}{67}\times\frac{18}{5} \)

    \( \displaystyle =\frac{360}{67} \)

    \( \displaystyle \approx5.37\ \text{km/hr} \)