Along a road there is an emergency telephone every 10 km, a water well every 15 km and a gas station every 20 km. How often do a telephone, a well and a gas station coincide?

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

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