I am working to find values and uncertainty in it. By using formula for finding time of pendulum i have to find value of acceleration due to gravity "g". The data is
Q :
find the value and uncertainty in value of g by using formula . t= 2pi*squart root of ( l/g).the length of simple pendulum is 100cm measured by metre rule of least count 0.1cm.time of 20 vibrations of pendulim is 40.2sec with stop watch of least count 0.1sec.find value and uncertainty in value of g

I suggest that you first work through the value of g that you get using the nominal values of L=100cm and T=40.2/20. Then see what happens if you vary L by plus-or-minus 0.05 cm and 40.2 seconds by plus-or-minus 0.05 seconds. One other hint: L must be in meters for the calculation of g to result in units of m/s^2.