Question

In a kindergarden class of 19 students, 100 addition problems can be completed in a mean time of 6 minutes. The

standard deviation is 1 minute.

How many students will finish before 5 minutes?

Answer 1

3

Explanation:

Answer 2

3 students

Explanation:

Two ways you can do this:

1. If you have a graphic calculator you can find the normal distribution function and enter the following values to get the probability of a student finished in less than 5 minutes:

Lower: 0

Upper: 5

Standard Deviation: 1

Mean: 6

This gives a probability of: 0.1587 (4.d.p)

2. You can use the formula and find the probability using the Z-table.

`Z = (x - \mu)/(\sigma)`

Substitute known values:

`Z = (5 - 6)/(1)\\Z = -1/1 = -1\\`

It is one standard deviation to the left of the mean,.

Look up on Z-score table and we get: 0.1587 (4.d.p)

Now we need to find expected number. We do this by multiplying the probability by the amount of people:

0.1587 x x19 = 3.0153 rounded to 3 students.

Hope this helped!