Question

A person on a diet might lose 2.3 kg per week. Express the
mass loss rate in milligrams per second, as if the dieter could
sense the second-by-second loss

Answer 1

1 kg = 1000000 mg
2.3 kg = 2.3*1000000 = 2300000 mg

1 week = 7 days
1 day = 24 hours
1hour = 3600 seconds

1 week = 7*24*3600 = 604800 seconds

2.3kgs/1 week = 2300000mgs/604800 sec = 3.803 mgs/1sec (approximately)

The person loss:
3.803 milligrams per second