The total distance he travelled in kilometer is 8.2 km
Distance is the total movement of an object without any regard to direction.
Given:
On Monday he walked = 1, 200, 000 mm
On Tuesday he walked= 2,400 m
On Wednesday he walked = 4.6 km
As, 1mm = 1/100,000
1,200,000 mm = 1.2 Km
and, 1 m =1/1000 km
2400m = 2.4 km
Hence, the total distance he travelled = 1.2+ 2.4 + 4. 6 = 8.2 km
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