問數學

1a2b3c4z

A jogging trail was 3km long.  Mary and Steve's average speed was 3.2km/h & 2.8km/h respectively.  They started at the starting point, but Mary started 3min after Steve.  How long until he caught up with Steve ?

Ryan_baba

將他們的速度分別轉成m/s就好易計

jane-wang

几年级的数学题？学方程没有？

81545

回覆 1a2b3c4z 的帖子

1) Steve's walking distance after 3 min = 2800/60 x 3 min = 140 metres
2) Let the minutes be X,

3200X/60 = 2800X/60 +140
400X/60 = 140
X = 21

yeesumyin

Because Steve had run for 2.8km x 3/60 = 0.14km, so the distance between Steve and Mary was 0.14km after 3 mins.  As Mary could run 0.4km more than Steve in an hour, so the formula is:
2.8km x 3/60 / 0.4 x 60
= 21min.