Question

The answer to this question 180, but how?

Answer 1

I'm going to show you two ways to do it.
Way #1 is the slogging way.
Way #2 is the clever way.


Way #1:

' One hundred percent ' means ALL of something.
ALL of the students in the school is the same as 100% of them.
If 10% are absent, then 90% are present.
90% means  0.9  .

                               1620 students  =  90% of the school.

                                            1620  =  0.9 x school total

Divide each side by 0.9:     1620/0.9 = total school

                                             1800  =  total school

How many were absent ? 
10% of them. 
10%  means  0.10  .

                         0.10  x  1800  =  180 students absent .
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Way #2:

' One hundred percent ' means ALL of something.
ALL of the students in the school is the same as 100% of them.

==> If 10% are absent, then 90% are present.

==> The number of students present is  9 times  the number who are absent.

                                            1620 = 9 x the number absent

Divide each side by  9 :    1620 / 9  =    the number absent

                                       1620 / 9  =  180 absent .