Walking with 4/5 of my usual speed, I miss the bus by 7 minutes. What is my usual time?
Select.
A) 16 min	B) 26 min	C) 28 min	D) 20 min	E) 12 min

Rationale: "speed ratio = 1 : 4 / 5 = 5 : 4 time ratio = 4 : 51 - - - - - - - - 7 4 - - - - - - - - - ? è 28 answer : c"
Answer: C