To find the ratio first we will be converting 25 km into 500m
=25*1000
=25000m
=25000:500
now 2 zero will be cut
250:5
now 250 is divisible by 5 ,so we will be dividing both
=250/5=50
now instead of 5 there will be 1 because we have done division
=50m:1m is the answer.