• So you can say —
In a 1500 metres race people run _________ km
In a 3000 metres race people run _________ km

We know
1 km = 1000 m
Half km = 500 m
Now,
1500 m = 1000 m + 500 m
= (1000$÷$1000) km + 500 m
= 1 km + Half km
= 1 and a half kilometres

In a 1500 metres race people run 1 and a half km

3000 m = (3000$÷$1000) km
= 3 km
In a 3000 metres race people run 3 km