请教一道四年级补习数学题

karenbj

Patrick was running in a 500 m race. He ran 300 m in 50 seconds and walked the remaining distance. If he took 150 seconds in total to finish the race, what was his average speed?

Answer from school:
speed for 300 m = 300 ÷ 50 = 6 m/s
speed for remaining = 500-300=200
200 ÷ 100 = 2 m/s
therefore, (6+2) ÷ 2 = 4 m/s  (补习学校答案是4 m/s)

可是，我老公就是认为不对
他说应该用 500 ÷ 150 = 3.33 m/s

到底哪个对呢？我也迷糊晕了

rachelwang528

你老公是对的。

ericcheung17

当然是3。33333

redragonfly

4m/s

千叶

你lg

largepa

哪个补习学校？不能去啊

SUORINA

Your husband is right 3.33m/s.

wqw

仔细看题！150 secs in total！当然是4m/s!

rachelwang528

wqw 发表于 2015-3-4 06:38
仔细看题！150 secs in total！当然是4m/s!

？？？ 请解释

maxiaoc

误人子弟啊！

qyz225

这数学是体育老师教的吧

karenbj

largepa 发表于 2015-3-4 03:20
哪个补习学校？不能去啊

著名的pre-uni

seecloud

wqw 发表于 2015-3-4 06:38
仔细看题！150 secs in total！当然是4m/s!

??？
当然补习学校的答案错了，
但这么容易的题都错还不至于吧

Xinjian

这个题体育老师都不会做错，这个补习学校误人子弟。你老公是对的。

feilafeila

3.3333333333吧
如果真的答案是4的话，我觉得要不就是我的英语出了问题，要不就是我的三观出了问题

PACIFIC

前面300米是6 m/s
后面200米是2 m/s

补习学校能把它们平均成4，我也是醉了

lxn_xiao

就看是average speed还是average of speeds

yourock

Arithmetic mean[edit]

Main article: Arithmetic mean

The most common type of average is the arithmetic mean. If n numbers are given, each number denoted by ai, where i = 1, …, n, the arithmetic mean is the sum of the ai's divided by n or
AM = \frac{1}{n}\sum_{i=1}^na_i = \frac{1}{n}\left(a_1 + a_2 + \cdots + a_n\right)
The arithmetic mean, often simply called the mean, of two numbers, such as 2 and 8, is obtained by finding a value A such that 2 + 8 = A + A. One may find that A = (2 + 8)/2 = 5. Switching the order of 2 and 8 to read 8 and 2 does not change the resulting value obtained for A. The mean 5 is not less than the minimum 2 nor greater than the maximum 8. If we increase the number of terms in the list to 2, 8, and 11, the arithmetic mean is found by solving for the value of A in the equation 2 + 8 + 11 = A + A + A. One finds that A = (2 + 8 + 11)/3 = 7.

tooheys_new

老师太强了

FloraShao

不是3.33嘛？？？？

gaddafi

要不就是这个英语表达有问题，记得英文里面有好几种表达类似平均速度的，中位数，平均值啊什么的，这个4不是平均值吧

sunnybear

你让老师以4m/s的速度跑500m，看看跑完是不是150s就知道了

枫丹白露

感觉这道题把简单的复杂化了，实际就是3.33啊

raoliang0082

你老公是对的。

emeraldpiggy

average speed is 4 m/s, it took  150 seconds to finish the race
the total length of the race is 4*150 = 600  m
:)

aqv

4 m/s not make sense

raoliang0082

哪个补习学校?

emeraldpiggy

http://math.stackexchange.com/qu ... ing-only-velocities

it clearly gives you the answer. you are calculating the velocity. not distance

Xinjian

速率的概念出来了，下面该说说矢量和标量的区别了。

mikey

yourock 发表于 2015-3-4 09:52
Arithmetic mean[edit]

Main article: Arithmetic mean

average speed is different from arithmetric mean. The definition of average speed is total distance/total time. So the coaching school's anwer is wrong.