The reaction times, t seconds, of 66 participants were measured in an experiment and presented below.

Time (t seconds) ......................              No. participants (cf )
t < 1.5 ................................................................... 0
t < 3.0 ................................................................... 3
t < 4.5 ................................................................... 8
t < 6.5 ................................................................. 32
t < 8.5 ................................................................ 54
t < 11.0 .............................................................. 62
t < 13.0 .............................................................. 66

a. Draw a cumulative frequency polygon to represent the data.

b. Use your graph to estimate:

i. The number of participants with reaction times between 5.5 and 7.5 seconds

ii. The lower boundary of the slowest 20 reaction times.