A certain element has a half life of 2.5 billion years. a. You find a rock containing a mixture of the element and lead. You determine that 20% of the original element remains; the other 80 % decayed into lead. How old is the rock? b. Analysis of another rock shows that it contains 65% of its original element; the other 35% decayed into lead. How old is the rock?

Two language majors, anna and megan, took exams in two languages. anna scored 85 on both exams. megan scored 74 on the first exam and 85 on the second exam. overall, student scores on the first exam had a mean of 82 and a standard deviation of 4, and the second exam scores had a mean of 71 and a standard deviation of 13. a) to qualify for language honors, a major must maintain at least an 85 average across all language courses taken. so far, which of anna and megan qualify? b) which student's overall performance was better?

Solve the triangle. a = 21°, c = 105°, c = 5

How do i put 3(x+7) in distributive property