.. Question 9 v ( ) A radioactive element decays into non-radioactive substances. In 420 days the radioactivity ofa sample decreases by 74 percent. Give your answer to me following questions round to the nearest whole number of days. (a) what is the half-life of the element? {is} How long will it take for a sample of 100 mg to decay to 6? mg? 0 Question 10 v ( ) Students in a fifth-grade class were given an exam. During the next 2 years, the same students were retested several times. The average score was given by the model t) 2 81 2010g[t + 1], 0 g 1' g 24 wheret is the time in months. Round answers to 'I decimal place. [a] What is the average score on the original exam? {b} what was the average score after 12 months? {0 After how man).r months does the average score drop below 55? l l m on ths . Question 11 The pH scale for acidity is defined by pl = - log , H* ] where [H ] is the concentration of hydrogen ions measured in moles per liter (M). (A) The pH of Milk of Magnesia is 10.5. Calculate the concentration of hydrogen ions in moles per liter (M). [H + ] = M (B) The pH of beer is 4.0. Calculate the concentration of hydrogen ions in moles per liter (M). [H +] = M