Given $$g = {{4{p^2}L} \over {{T^2}}}$$

Fractional error in value of g

$${{\Delta g} \over g} = {{\Delta L} \over L} + 2{{\Delta T} \over T}$$

$$ \Rightarrow {{\Delta g} \over g} \times 100 = {{\Delta L} \over L} \times 100 + 2{{\Delta T} \over T} \times 100$$

$$ \Rightarrow {{\Delta g} \over g} \times 100 = {{0.1} \over {10}} \times 100 + 2 \times {1 \over {100}} \times 100 = 3\% $$

Hence, percentage error in measurement of g is 3%