Question

planets a, b and c orbit a certain star once every 3, 7, and 18 months respectively. if the three planets are now in the same straight line, what is the smallest number of months that must pass before they line up again?

Answer 1

basically, what is the smallest number which all can multiply to

3=3
7=7
18=2*3*3

2*3*3*7=126

answer is 126 months