Prep-T2-Q166-PS

[hibiscus]

166.
70, 75, 80, 85, 90, 105, 105, 130, 130, 130
The list shown consists of the times, in seconds, that it took each of 10 schoolchildren to run a distance of 400 meters. If the standard deviation of the 10 running times is 22.4 seconds, rounded to the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times?

(A) One
(B) Two
(C) Three
(D) Four
(E) Five

答案....B

我怎麼算答案就是A
請大大幫幫忙吧
我快要考試了...
謝謝

[plilo]

the mean of the 10 running times is 100

100-22.4=77.6

70, 75 <77.6

所以有 2個

[gozui[origen]]

how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times?

關於這句話, 我怎麼看都覺得是在問有幾個數是 大於 100-22.4
"1 standard deviation below the mean"的意思不是 100-22.4, 也就是77.6 嗎?
"more than"不就是比 77.6大嗎?

一直很納悶答案選項中為什麼沒有"8"?

想請問你們是怎麼理解這個句子的...

[plilo]

這是在問有幾個數是超過SD=1的區間，
以mean 為中心，SD=1的範圍在77.6~122.4
問題問below，所以是找比77.6小的數

[gozui[origen]]

了解了
非常感謝plilo