To find the median cancel out numbers on both sides, until one is left in the middle and if there are two in the middle add them up and divide by two.
So in this case the median is
53+78
131 / 2
65.5
54%
Just divide 450 out of 828
450/828= 0.54347
Move the decimal to the right twice
5/6 x 18
=90/6
=15
5/6 of 18 pencils equals 15.