(⊙o⊙)数学题选择并解释Yourbrotherstartsout10minutesbeforeyouonabikepathanridesatarateof9milesperhour.Ifyourideatarateof12milesperhour,howlongwillittakeyoutocatchuptohim?A:1/4hourB:1/2hourC:2/3hourD:

Question

(⊙o⊙)数学题选择并解释
Your brother starts out 10 minutes before you on a bike path an rides at a rate of 9 miles per hour.If you ride at a rate of 12 miles per hour,how long will it take you to catch up to him?
A:1/4hour
B:1/2hour
C:2/3hour
D:3/4hour
9/6 = 12t - 9t
First,your brother and you are riding a bike.
Your brother rides out first on his bike and he has a 10 minute head start.
Your brother rides slow,at 9 miles per hour.
You,on the other hand,ride fast,at 12 miles per hour.
We want to know how long will it take for you to catch with your brother.That is,both of you at the same
distance!
Your brother = You
9 miles/hour (t + 1/6 hour ) = 12 miles/hour (t)
Tips:1/6 hours is same as 10 minutes in terms of an hour
Tips:t is our variable that will answer the question.
Lets solve:by distributing property
9t + 9/6 = 12t
9/6 = 12t - 9t
Finally,we are here.You will now combine like terms and solve for the value of

Answer 1

你哥时速9mlies/h,先走10分钟,领先你9*10/60=1.5miles
你时速12,追你哥,速度差为12-9=3miles/h,
追上需要的时间为1.5/3=1/2h
选B