It takes 20 s for a girl A to climb up the stairs while girl B takes 15 s for the same job. Compare:

(a) The work done and

(b) The power spent by them.

(a) Both the girls move the same distance and force is also equal on both. Hence, the work done by both the girls is the same.
∴ Work done by girl A : Work done by girl B = 1 : 1

(b) Power spent = $\dfrac{\text{Work done}}{\text{time taken}}$

We know,

Work done by girl A = Work done by girl B = W

Power spent by girl A (P_A) = $\dfrac{\text{W}}{\text{20}}$

Power spent by girl B (P_B) = $\dfrac{\text{W}}{\text{15}}$

Comparing the power spent by girl A and girl B:

$\dfrac{\text{P}_\text{A}}{\text{P}_\text{B}} = \dfrac{\dfrac{\text{W}}{\text{20}}}{\dfrac{\text{W}}{\text{15}}} \\[1em] = \dfrac{\text{15}}{\text{20}} = \dfrac{\text{3}}{\text{4}}$

∴ Power spent by girl A : Power spent by girl B = 3:4.