plain a is traveling at a speed of 500 mph plane b is traveling 45mph slower than plain a when will plain a and plain b pass each other
First let's assume that d0 miles is initial distance between two planes.
1. Both planes are traveling toward to each other with speed (500 + (500-45)) = 955 mph, and they will pass each other in (d0/955) hours.
2. Both planes are traveling in opposite directions with 955 mph and they will never "meet" each other.
3. Plane a "tries to catch" plane b and it will happen in d0/(500-455) = d0/45 hours.
4. Plane b (slower moving one) "tries to catch" plane a .... and it will never happen.