What is the substitution method?

The cost of using a service is $0.25 per min. what equation correctly represents the total cost c, in dollars, for d days of use?

Ur environment is very sensitive to the amount of ozone in the upper atmosphere. the level of ozone normally found is 4.04.0 parts/million (ppm). a researcher believes that the current ozone level is not at a normal level. the mean of 2525 samples is 4.44.4 ppm with a standard deviation of 0.80.8. assume the population is normally distributed. a level of significance of 0.020.02 will be used. make the decision to reject or fail to reject the null hypothesis. answer tables

Tom says that he needs 6 rolls to obtain each possible outcome on a 6-sided die. on the fourth roll, he rolls his second "3”. tom says that the die is loaded and that each outcome is not equally likely. is tom correct here? if you think tom is incorrect, how many rolls should tom make until he sees each number occurring about 1/6 of the time?