Question

A simple pendulum takes 42 seconds to complete 20 oscillation that time period is

Answer 1

Frequency=
$20 \div 42 = 0.47$
time period=
$1 \div 0.47 = 2.127$

Answer 2

No. of oscillations completed by the pendulum= 42 

Time taken to complete 42 oscillation= 20 seconds 

Time period= No. of oscillations completed/Time taken 

Time period= 42/20 

= 21/10 (cancelled by 2) 

= 2.1 

Time period= 2.1 seconds