Initial temperature = 40°C
Room temperature decreases at 5°C per hour
Temperature change in 1 hour = -5°C
Temperature change in 10 hour = -5 × 10°C = -50°C
Room temperature after 10 hours = Initial temperature + Temperature change in 10 hour
= 40 + (-50)
= 40 – 50
∴ Room temperature after 10 hours = -10°C