Question 310508
 On the first night 12 choir members were absent, so the choir stood in 5 equal rows. 
On the second night only 1 member was absent so the choir stood in 6 equal rows.
 The same number of people stood in each row each night.
 How many members are in the choir?
:
Let x = no. in the choir
:
1st night in a row = 2nd night is a row
{{{(x-12)/5}}} = {{{(x-1)/6}}}
Cross multiply
6(x-12) = 5(x-1)
6x - 72 = 5x - 5
6x - 5x = -5 + 72
x = 67 members in the choir
:
:
Check by finding the no. in a row in each scenario
{{{(67-12)/5}}} = 11
{{{(67-1)/6}}} = 11