Let

denote the number of minutes spent brushing his teeth, and let

be the mean and

the standard deviation for this distribution.

The z-score corresponding to this probability is approximately

, which means

Next, (note the sign change)

The corresponding z-score is approximately

, so you have

Solving the two equations for

and

, you'll find that the mean is approximately

and the standard deviation is approximately

.
Answer:
y = 23
Step-by-step explanation:
The diagonals of a rhombus are perpendicular bisectors of each other, thus
∠1 = 90° and ∠1 = 4y - 2, so equating gives
4y - 2 = 90 ( add 2 to both sides )
4y = 92 ( divide both sides by 4 )
y = 23