Question

1 inch = 2.54cm 1 mile = 1.6km a map has a scale of 1 inch represents 1 mile use the given conversions to show that 1cm on the map represents approximately 0.6km

Answer 1

Note: 1 inch = 2.54 cm is an exact converion, while 1 mile=1.6km is only approximate.

Using conversion
1 inch=2.54 cm
1 mile = 1760*3*12 = 63360 in = 160934.4 cm 
If 1 inch = 1 mile, then 
2.54 cm : 1 mile = 1.609344 km
1 cm : 0.6336 km   (exactly), or
1 cm : 0.6 km (approximately)

Using both conversions:
1 inch = 2.54 cm : 1 mile = 1.6 km
=>
2.54 cm : 1.6 km
1 cm : 1.6/2.54=0.6299 km (approximately), or
1 cm : 0.6 km (approximately)