Actually, I would question if this is really a histogram as a histogram groups numbers into ranges and doesn't duplicate the range. See
here
.
You are incorrect in thinking about this histogram as a single source. The question clearly reads,
"You then created the following resource histogram for your staff.". This means that each week is utilization for the entire staff. Again, this is a great PMP-thinking question because you probably wouldn't really create graphs this way because it loses fidelity. But we can glean from the chart, that in weeks 8 and 9, when the utilization is 150% that that number represents the utilization of ALL those assigned to do work that week. This makes the graph a little bit fuzzy since it is not a count like a true histogram, its a percentage, which is based on some theoretical limit of what work could be accomplished in that week. Thus, we are trying to cram 50% more work in week 8 and 9 than is physical possible within a normal work-week.
As always, free questions, may not be vetted and peer reviewed that well and this one clearly could use some work. But it definitely shows how to approach these questions on the PMP exam. We don't pick the answer we would like it to be, we pick the best (or least-worst) of those questions remaining. Or as Sherlock Holmes says, "When you have eliminated the impossible, whatever remains, however improbable, must be the truth."
Wanted to just clear up your response slightly.
Hope this helps.