You asked about the rule governing the choice of the verb in the following
sentence:
 
"It was one of those jobs that (takes, take) much more time than you expect.
The choice here is take, the plural verb. The subject that dictates the choice
is jobs, although, as is indicated, many people choose takes, erroneously
believing that one is the subject of the verb. Note, however, that there are
two clauses: a main clause, It was one and a subordinate clause of those jobs
that take. One can be viewed as a subjective complement. In the subordinate
clause, that refers to jobs, deriving this sequence: jobs + that + take. . .
Another way of solving the problem is to reverse the sentence: Of the jobs
that take much more time than you expect, it is one.
A subtle modification of the sentence would yield takes:
"It was the only one of the jobs that takes much more time than you expect."
The inclusion of makes the verb singular.
 
                                                  Rudolph Brathwaite