On the basis of extensive tests, the yield point of a particular type of mild steel-reinforcing bar is known to be normally distributed with σ = 100. the composition of bars has been slightly modified, but the modification is not believed to have affected either the normality or the value of σ. (a) assuming this to be the case, if a sample of 25 modified bars resulted in a sample average yield point of 8439 lb, compute a 90% ci for the true average yield point of the modified bar. (b) compute a 92% ci for the true average yield using the sample data in (a).

Step-by-step explanation:

Given that the yield point of a particular type of mild steel-reinforcing bar is known to be normally distributed with σ = 100

Modified mean without change of sigma = 8439

Sample size n =25

Std error of sample =

For 90% confidence interval we use Z critical value since we know population std deviation

Margin of error =

a) Confidence interval

=

b)For 92% critical value changes to 1.75

Confidence interval

=

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step-by-step explanation:

if gloria has "carry over" minutes, (that is, any minutes paid for but not used in a month can be applied to her payment for minutes in the next month,) her total usage for the three months is: total minutes = 320 + 243 + 489 = 1052 minutes number of 200 minute blocks = 1052/200 = 5 r52 (that is 5 with a remainder of 52) rounding up the number of 200 minute blocks gives her usage for the three months as 6 blocks. the cost for six blocks is 6 x $25 = $150 she also has 200 - 52 or 148 carry over minutes if gloria pays each month and unused minutes are lost, applying the rounding up procedure to each month gives: first month usage of 320 minutes rounds up to 2 blocks of 200 minutes for a payment of 2 x $25 = $50 second month usage of 243 minutes rounds up to 2 blocks of 200 minutes for a payment of 2 x $25 = $50 third month usage of 489 minutes rounds up to 3 blocks of 200 minutes for a payment of 3 x $25 = $75 total payments for the three months are $50 + $50 + $75 = $175 get the plan with carry over minutes!