+45 Alex, Blake, and Christine are running on a 400 meter track at constant speeds. Alex and Blake are running in the same direction, but Christine is running in the opposite direction. Christine passes Alex every 40 seconds and passes Blake every 50 seconds. If Blake is passed by Alex every x seconds, what is the value of x?
A street has 20 houses on each side, for a total of 40 houses. The addresses on the south side of the street form an arithmetic sequence, as do the addresses on the north side of the street. On the south side, the addresses are 4, 10, 16, etc., and on the north side they are 3, 9, 15, etc. A sign painter paints house numbers on a house for $1 per digit. If he paints the appropriate house number once on each of these 40 houses, how many dollars does he collect?
