how many positive integers less than 400 are divisible by both 7 and 11?
how many perfect squares less than 1000 have a ones digit of 2, 3 or 4?
a solar system contains four planets and a sun as shown. planet A completes an orbit around the sun in 20 months; planet B completes an orbit in 36 months; planet C completes an orbit in 40 months; and planet D completes an orbit in 48 months. If the four planets lie along a straight line in May of the year 2000, what is the next year that they will again lie along the same line? Assume that the orbits are circular and that a year has exactly 12 months.