A machine operator can program machine #1 to produce 100 parts per hour, but the machine requires 2 hours of service each day when it is not operating. Machine #2 can produce only 80 parts per hour, but only requires 30 minutes of service each day. Which machine is more productive in an eight-hour workday?

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.'

answer; coefficient of correlation;