Answer:
The answer is 600 minutes (10 hours)
Step-by-step explanation:
20 minutes = 1 student.
30 students x 20 = 600 minutes
600mins / 60 (because an hour has 60 mins) = 10 hours.
Box 1 : 3 pencils + 7 pens = total of 10
probability of picking a pen is 7/10
box 2 : 3 pencils + 3 crayons = total of 6
probability of picking a crayon is 3/6 which reduces to 1/2
probability of picking both is (7/10 * 1/2) = 7/20 <==
-10 is the correct answer