An automobile travels for 80 minutes at 70 mph, 15 minutes at 65 mph, and 5 minu

Question

An automobile travels for 80 minutes at 70 mph, 15 minutes at 65 mph, and 5 minutes at 50 mph. What is the average speed? 50-64.5 mph 65-66.5 mph 67-68.5 mph 69-70 mph Chlorine Cl, consists of two isotopes only. The predominant isotope, Cl-35, is about 76% of the total with a mass of about 35 amu. The other isotope is Cl-37, 24% of the total, having a mass about 37 amu. Which of the following is a correct calculation for the average isotopic mass of Cl? Isotopic mass = 35 amu Isotopic mass = (35 + 37)/2 = 36 amu Isotopic mass = (35 times 76%) + (37 times 24%) = 3548 amu Isotopic mass = (35 times 0.76) + (37 times 0.24) = 35.48 amu Gallium, Ga has two isotopes and an average mass of 69.8 amu. In what proportion are the two isotopes of gallium? 50%^69Ga and 50%^71Ga 10%^69Ga and 90%^71Ga 40%^69Ga and 60%^71Ga 60%^69Ga and 40%^71Ga

Explanation / Answer

14) Average speed = total distance travelled / time of travel
for 80 min = 70 miles / hr * (80/60) hr = 93.3333 miles
   for 15 min = 65 miles / hr * (15/60) hr = 16.25 miles
   for 5 min = 50 miles / hr * (5/60) hr = 4.1667 miles
   total distance travelled = 113.75 miles
total time taken to travel 113.75 miles = (80/60) hr + (15/60) hr + (5/60) hr = 1.6667 hr
Average speed = 113.75 miles / 1.6667 hr = 68.25 mph
So third option, i.e) 67-68.5 mph is the right answer.

15) Isotopic mass will be (35 * 0.76) + (37*0.24) = 35.48 amu
   Last option is the correct answer.

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