Question

Add 5 ft 9 in and 10 ft 11 in

Answer 1

Add the feet together and add the inches together.

5 ft + 10 ft = 15 ft
9 in + 11 in = 20 in

Now there are only 12 inches in a foot so we have more than a foot in inches so we move 1 foot over so we have

16 ft 8 inches

Answer 2

We know that 1 foot is 12 inches then, we change all quantities to inches to ease the calculations:
5 ft 9 in = 5(12) + 9 = 60 + 9 = 69 inches
10 ft 11 in = 10(12) + 11 = 120 + 11 = 131 inches
so we add:
5 ft 9 in + 10 ft 11 in
= 69 inches + 131 inches
= 200 inches
if we want the result in foot we divide:
= 200/12
= 100/6 = 50/3
= 16 ft 8 in