Answer:
60 km
Step-by-step explanation:
Given that :
Location of emergency telephone = every 10km
Location of water well = Every 15 km
Location of gas station = every 20 km
To obtain how often an emergency telephone, water well and gas station coincide, we obtain the lowest common multiple of 10, 15 and 20
Multiples of ;
10 : 10, 20, 30, 40, 50, 60, 70
15 : 15, 30, 45, 60, 75, 90, 105
20 : 20, 40, 60, 80, 100
Hence, the lowest common multiple of 10, 15 and 20 is 60, thus, an emergency telephone line, gas station and water well will coincide every 60km
