A man travelled a distance of 80 km in 7 hours partly on foot at the rate of 8 km per hour and partly on bicycle at 16 km /hr. Find the distance travelled on foot?

Let the distance travelled on foot be x km

Then the distance travelled on bicycle = 80 - x km

Speed on foot = 8 km/h ⇒ Time on foot = x / 8 hours

Speed on bicycle = 16 km/h ⇒ Time on bicycle = (80 - x) / 16 hours

Total time = 7 hours

x / 8 + (80 - x) / 16 = 7

Step 1: Multiply through by LCM (16) to eliminate denominators:

2x + (80 - x) = 112
=> 2x + 80 - x = 112
=> x + 80 = 112
=> x = 32

Answer: 32 km was travelled on foot.