Answer:

It is simply calculation of scale,and scale of the map is DEFINED as “ratio of a distance on the map to the CORRESPONDING distance on the ground.”

Scale of map=distance on the map/distance on the ground.(unit of map and ground distance must be same.)

According to QUESTION,1 cm on the map distance equal to 5 km on the ground distance.

Step 1:-convert one of them in single unit, either cm convert into km or vice VERSA.

(I converted km into cm)

5km*1000=5000m

5000m*100=500000cm. (1)

Step 2:-put the value in the formula of scale of map.

Distance on map=1cm

Distance on ground=500000

Then,

Scale of map=1/500000…(ii)

Now, move to another portion of the question where the distance on the ground are given, that is 20km.

Step 3:-convert 20km to cm scale

20km*1000=20000m

20000m*100=2000000cm. (iii)

Scale of map=distance on map/distance on ground.

Then, distance on map=scale of map*distance on ground. (By cross multiplication)

From equation (ii) and (iii) put the values:-

Distance on map=1/500000*2000000cm

Distance on map=4cm