Two simple pendulums of lengths I m and 16 m respectively are both given small displacements in the same direction at the same instant. They will again be in phase after the shorter pendulum has completed n oscillations where n is:

Let shorter pendulum makes n vibrations then longer makes (n-1) vibrations to come in phase again then nT1=n-1T2                                                                                                                                          nn-1=T2T1=161=4⇒n=43