City L and City M are 420 km apart. At 3.50 p.m., Oscar is travelling at a uniform speed left City L for City M while David set off from City M to City L along the same road at a uniform speed, which was 6 km/h slower than that of Oscar. The two met at 5.50 p.m.
- Find the speed of Oscar.
- If David continued to travel at the same speed, how long would it take for him to reach his destination after the two met? Express your answer in mixed number.
(a)
Time taken for Oscar and David to travel from 3.50 p.m. to 5.50 p.m. = 2 h
Average speed of Oscar and David
= 420 ÷ 2
= 210 km/h
Oscar's speed
= (210 + 6) ÷ 2
= 216 ÷ 2
= 108 km/h
(b)
David's speed
= 108 - 6
= 102 km/h
Distance that David travelled in 2 h
= 2 x 102
= 204 km
Remaining distance that David needed to travel
= 420 - 204
= 216 km
Time that David needed to reach his destination after the two met
= 216 ÷ 102
= 2
12102 = 2
217 h
Answer(s): (a) 108 km/h; (b) 2
217 h