What makes the difference between 250 slides and 300 slides?

•   The difference is that 50 additional slides were added to the 250 slides to cover new subjects such as Convergence, Number Portability, 3G systems, Wimax, Co-location of telecommunications infrastructure and a few new developments in the industry in Nigeria and worldwide in the second half of 2008.
  -  The material actually started in 2003 with 100 slides, went higher to 150 in 2005, to 250 in 2007 and 300 in 2009