Tom ran around a ring track,which is 360 meters.During the first half of the whole time,his speed was 5 meters every sec
Tom ran around a ring track,which is 360 meters.During the first half of the whole time,his speed was 5 meters every second.During the second half,his speed was 4 meters every second.How many seconds did he spend on the second half of the whole way?
數(shù)學(xué)人氣：694 ℃時(shí)間：2020-04-24 22:17:48
優(yōu)質(zhì)解答
速度乘以時(shí)間等于路程,總路程是360米,前半段時(shí)間的速度是每秒5米,后半段是每秒4米.由于Tom跑每秒5米和每秒4米都用了總時(shí)間的一半,設(shè)總時(shí)間的一半為x,故前段路程等于5x（速度乘以時(shí)間）,后段等于4x（注：5x不等于一半路程,4x也是）.兩段路程合起來就是總路程,5x + 4x = 360.然后合并同類項(xiàng)和解方程,得x = 40.問題求的是后半段路程所用時(shí)間,路程的一半是180米.Tom最后用每秒4米的速度跑了4 × 40 = 160米,還有20米是用每秒5米的速度跑的,而這段一共是用了20 ÷ 5 = 4秒.這4秒加上后面換了速度跑的40秒,得出答案Tom一共用了44秒去跑后半段180米的路程.
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