Question 726525
The median is the number that is in the middle if you arrange the values in order. (If there is an even number of values you average the two in the middle).
It is a number such that half of the values are lesser or equal and the othe half are greater or equal.
In this case, you have 5 values, listed in order, and the middle one is {{{b=50}}}, the median.
The average (or arithmetic mean) is
{{{(a+a+b+c+c)/5=40}}}
so, multiplying both sides times 5, we get
{{{2a+b+2c=40*5}}} --> {{{2a+b+2c=200}}}
Substituting {{{b=50}}},
{{{2a+2c+50=200}}} --> {{{2a+2c=200-50}}} --> {{{2a+2c=150}}} --> {{{2(a+c)=150}}} --> {{{a+c=150/2}}} --> {{{highlight(a+c=75)}}}