Question

The time to complete a standardized exam is approximately Normal with a mean of 70 minutes and a standard deviation of 10 minutes. Using the 68–95–99.7 rule, if students are given 90 minutes to complete the exam, what percent of students will not finish?
A. 32%
B. 5%
C. 2.5%
D. 0.0015%

Answer 1

I say C

Answer 2

90 mins is 2 deviations which leaves 2.5 %

Answer 3

Lol you're answering your own questions. Too op.

Answer 4

Like I said I'm bjust double checking myself if I'm wrong then it's easier tocorrect it :).

Answer 5

Was I correct on this one? C?

Answer 6

Lol i'm not even in standard devs yet. Only 17 lolz.

Answer 7

oh okay :)

Answer 8

I did this with calc 2, when byou try to answer it on your own it helps sink in.

Answer 9

@jim_thompson5910 :)

Answer 10

99.7% of the students will have times from 70-2*10 = 50 min to 70+2*10 = 90 min

(100 - 99.7)/2 = 0.15% will have times below 50 min

So 99.7+0.15 = 99.85% will have times below 90 min

This means that 100 - 99.85 = 0.15% of the students will not be able to finish the exam.

Answer 11

:O

Answer 12

however that isn't a choice.... 0.0015% is... LOL.

Answer 13

>(

Answer 14

I like the process... is 95 supposed to correspond to 2 standard deviations?

Answer 15

mhm

Answer 16

I keep getting my formulas konfused...

Answer 17

then it would be C using his process, but replacing 99.7 with 95.

Answer 18

oh right...lol my bad

Answer 19

99.7 is 3 std deviations away

Answer 20

95 is 2

Answer 21

I basically thoght 10 is the dev.

Answer 22

10 is the std dev

Answer 23

so then it's m + 2sigma

Answer 24

so 70+20 = 90 and that leaves 2.35 and .15

Answer 25

which is 2.5%

Answer 26

So I was right >( no medals >(

Answer 27

;)