Question

It takes nora two hours to paint a wall 5m by 8m, and zack three hours to paint a wall 4m by 9m. together, how long will it take them to paint a wall 10m by 12m?

Answer 1

Nora's speed (5*8)m²/2h= 20 m²/h.
Zack's speed (4*9)m²/3h= 12 m²/h

Together for 1 h they paint (20+12) m²/h=32m²/h

Given area (10*12)m²=120 m²

120m² *1h/32m² = 3.75 h (3h 45 min) to paint 10m*12m together.