Question 412423
The fraction of 54 pupils that didn't use them once is:
{{{(2/3)*(1/4 + 1/3 + 2/9)}}}
{{{4*9 = 36}}} is the LCD and nothing smaller will work
{{{(2/3)*(9/36 + 12/36 + 4/36)}}}
{{{(2/3)*(25/36)}}}
{{{50/108 = 25/54}}}
This is the fraction of 54 pupils who DID NOT use it just once,
so the fraction who used it only once is:
{{{1 - 25/54 = 54/54 - 25/54}}}
{{{54/54 - 25/54 = 29/54}}}
The number of pupils who used them only once is {{{54*(29/54) = 29}}}