A certain radioactive isotope has a half-life of 50 years. A scientist determines that there are 200 grams of the radioactive material present today. How Much of the isotope was present 200 years ago?

65% of students in your school participate in at least one after school activity. if there are 980 students in you school, how many do not participate in an after school activity?

For the chance to be team captain, the numbers 1-30 are put in a hat and you get two chances to pick a number, without replacement. which formula correctly shows how to find the probability that you choose the number 1 and then 2?

Study results indicate that the mean length of time people spend on a bus in a city is between 21.2 min and 24.5 min what is the study margin of the error?