Determine the acceleration of gravity on the surface of Mars, provided that there a mathematical pendulum 50 cm

Determine the acceleration of gravity on the surface of Mars, provided that there a mathematical pendulum 50 cm long would make 40 oscillations in 80 s.

Given: l = 50 cm = 0.5 m;
n = 40 vibrations;
t = 80 s
Decision:
The oscillation period of the mathematical pendulum:
T = t / n = 80/40 = 2 s
Then we find the acceleration of gravity on the surface of Mars: T = 2Π * √ (l / g);
l / g = T2 / 4Π2g = l * 4Π2 / T2 = 0.5 * 4 * 3.142 / 22 ≈ 4.93 m / s ^ 2
Answer: g≈ 4.93 m / s ^ 2.