Two cyclist start from the same places in opposite directions. One is going towards north at 10kmph and the other is going towards south 10kmph. What time will they take to be 50km apart?
Choose one
A) 1.2 hr B) 2.5 hrs C) 3 hrs D) 5.2 hrs E) 6 hrs

Rationale: "to be ( 10 + 10 ) km apart , they take 1 hour to be 50 km apart , they take 1 / 20 * 50 = 2.5 hrs answer is b"
Answer: B