A recent review of an online electronics distributor's product line is summarized as follows:

Price (S)	# items Sold
0 to <5	44
5 to <10	175
10 to <15	222
15 to <20	319
20 to <25	234
25 to <30	134
30 to <35	23

Use the equation editor and appropriate summation notation, determine:

a) the mean

b) the median

c) range

d) interquartile range