The lifetimes of a certain brand of photographic are normally distributed with a mean of 210 h and a standard deviation of 50 h. What percent of lights will need to be replaced within 235 h? Show Work

69.15% of lights will need to be replaced within 235 h.

Step-by-step explanation:

We are given that the lifetimes of a certain brand of photographic are normally distributed with a mean of 210 h and a standard deviation of 50 h.

Let X = the lifetimes of a certain brand of photographic

The z-score probability distribution for the normal distribution is given by;

                              Z  =    ~ N(0,1)

where, = population mean lifetime = 210 h

            = standard deviation = 50 h

Now, the percent of lights that will need to be replaced within 235 h is given by = P(X 235 h)

      P(X 235 h) = P( ) = P(Z 0.50) = 0.6915 or 69.15%

The above probability is calculated by looking at the value of x = 0.5 in the z table which has an area of 0.6915.

its 4 because 2 times 2 is 4, if you double the number two you get four

2. angles qrt and qst both measures 156 degrees.

step-by-step explanation:  

we have been given a diagram of a circle and we are told that measure of arc qvt is 156 degrees.  

we can see from our given diagram that angle qrt and angle qst subtends to arc qvt.

since we know that angles subtended by the same arc at the circumference are always equal.

by angle subtended by same arc theorem, measure of angle qrt and angle qst will be equal to the measure of arc qvt.

therefore, angles qrt and qst both measures 156 degrees and 2nd statement is the correct choice.