Question 1156440
.
<pre>

Let n be the number under the question.


Then the cost per person is  {{{900/n}}}  in the first case, and  {{{900/(n+15)}}} in  the second scenario.


According to the condition,


    {{{900/n}}} - {{{900/(n+15)}}} = 10.


It is your basic equation.

To solve it, first cancel the common factor 10 in both sides


    {{{90/n}}} - {{{90/(n+15)}}} = 1.


You may solve it MENTALLY  n= 30.


Alternatively, you can reduce the given problem to a quadratic equation
and then solve it.


<U>ANSWER</U>.  30 members.


<U>CHECK</U>.  {{{90/30}}} - {{{90/(30+15)}}} = 3 - 2 = 1.
</pre>