Let, length of pendulum = L
Time period T=√Lg=1sec
Now, time in a day
t=1×60×60×24
Now, after increasing length o.1%
New length
L′=L+0.001L
Now, new time period
T′=√L′g
T′=√1.001Lg
T′=√1.001×√Lg
T′=√1.001s
Now, time in a day
t′=√(1.001)×60×60×24
Now, error in a day
=√(1.001)×60×60×24−1×60×60×24
=60×60×24(√(1.001)−1)
=60×60×24(1.0005−1)
=60×60×24×.0005
=43.2s
Hence, the error in time per day is 43.2 s