Preeti reached the metro station and found that the escalator was not working. She walked up the stationary escalator in time $t_1$. On other days, if she remains stationary on the moving escalator, then the escalator takes her up in time $t_2$. The time taken by her to walk up on the moving escalator will be

• A

  $\frac{t_1+t_2}{2}$
• B

  $\frac{t_1{t}_2}{t_2-t_1}$
• Correct answer
  C

  $\frac{t_1{t}_2}{t_2+t_1}$
• D

  $t_1-t_2$

Hence, the correct answer is option: 'C'.