What is the total mass of all the people on earth?
It is impossible, of course, to give an accurate answer to this question. However, it is quite possible to find the order of magnitude of the answer. All one needs to do is to use some common sense and, possibly, search for relevant reference information. The calculation can proceed as follows:
There are about 6×109 people on earth. An average adult male weighs, say, 75 kg; an average adult female weighs about

Question

What is the total mass of all the people on earth?
It is impossible, of course, to give an accurate answer to this question. However, it is quite possible to find the order of magnitude of the answer. All one needs to do is to use some common sense and, possibly, search for relevant reference information. The calculation can proceed as follows:
There are about 6×109 people on earth. An average adult male weighs, say, 75 kg; an average adult female weighs about

anonymous · Answer

60 kg, and an average child will weigh considerably less than 60 kg. Figuring roughly one child per adult, we can reasonably say that an average person's mass is about 50 kg, which gives the total mass of all humans on our planet as
6×109×50=3×1011kg.
Of course, we may be off in our estimates of the average mass or number of people. Although it would be unreasonable to say that we know the total mass is 3.0×1011kg, we can be reasonably sure that we have the correct order of magnitude; that is, we have the correct exponent to which the number 10 is raised.
In each of the following problems, you will be asked to make similar estimates.