Shawn is planning a bus trip across town that involves three buses. bus 1 travels between shawn’s house and downtown, and it leaves every half-hour starting at 7: 20 am. shawn will need to be on bus 1 for 1.2 hours. bus 2 travels between downtown and uptown every half-hour starting at 7: 10 am. shawn will need to be on bus 2 for 2/3 hour. lastly, bus 3 travels between uptown and shawn’s destination every hour starting at 9 am. assuming all buses stay on schedule, what is the least amount of time shawn must spend waiting for buses?
(a) 12 minutes
(b) 18 minutes
(c) 48 minutes
(d) 1 hour, 12 minutes
(e) 1 hour, 20 minutes

least waiting time = 18 mins

Explanation:

given as per question we know that 2nd bus start 10 min early than 1st bus

and both time frequency same = 30 min

1st bus time take = 1 hr 12 mins

and 2nd bus get waiting time 30 min - (10 + 12)

that is = 8 mins

so

we can say  time arrival time for 1st bus = 8:32 and 9:02  and 9:32

by adding 30 mins

and

departure time for 2nd bus =  8:40 and 9:10 and 9:40

same like that 3rd bus leave every hour

and

service start on hour clock , a 10 mins early is = 7:10 am and 9 am

frequency of either half or 1 hour

so 2nd bus takes =  2 hour 40 mins

so waiting time is 60 - (10 - 40) = 10 min or 10 + 30 = 40 mins

so 1st bus waiting time is 8 mins so it take least time 10 mins for 2nd bus waiting time

as that

least waiting time = 8 + 10

least waiting time = 18 mins

idk the answer so dont listen to me but 23

ans.

heterothermic organisms include those organisms that can switch between homeothermic (having body temperature higher than environment) and poikilothermic (having variation in internal body temperature) strategies.

some migratory birds show heterothermy as they decrease their metabolic rate during cold nights to keep their body temperature low. drop in metabolic rate allows increase in production efficiency of birds that reduces the internal body temperature to make it equal to external cold temperature during cold nights.

thus, the correct answer is 'birds allow their temperature drop in order to increase their production efficiency.'