The formula for the period T of a pendulum is T = 2π Square root of√L/g, where L is the length of the pendulum and g is the acceleration due to gravity.
2/3 multiples by 3 in both the numerator and denominator is equal to 6/9. 6/9 plus 5/9 is 11/9. you want to make sure the denominator is the same before adding or subtracting
