In this problem, we are given that Mr. Murphy has 2 boxes of pens in his office, with 5 bundles of pens in each box, and 50 pens in each bundle. We can find the total number of pens Mr. Murphy currently has by multiplying the number of boxes by the number of bundles in each box, and then by the number of pens in each bundle. This gives us:
2 boxes x 5 bundles per box x 50 pens per bundle = 500 pens
Next, we are told that Mr. Murphy wants to have 750 pens available for the fundraiser. To determine how many more pens he needs to order, we can subtract the number of pens he currently has from the total number of pens he wants to have:
750 pens - 500 pens = 250 pens
This tells us that he needs to order 250 more pens to have a total of 750 pens available for the fundraiser.
Mr. Murphy currently has 500 pens in his office because 2 x 5 x 50 = <<2*5*50=500>>500.
Mr. Murphy needs to order 250 more pens because 750 - 500 = <<750-500=250>>250.
Therefore, Mr. Murphy should order 250 more pens.