What are systematic errors and random errors?

I need help with the question please: Some students decided to test whether drinking caffeine would affect heart rate. They asked the class to help them with their investigation. They divided the class into two groups. Both groups had their pulses taken. They gave one group a drink of coffee. They waited for 10... show more I need help with the question please:
Some students decided to test whether drinking caffeine would affect heart rate. They asked the class to help them with their investigation. They divided the class into two groups. Both groups had their pulses taken. They gave one group a drink of coffee. They waited for 10 minutes and then took their pulses again. They then followed the same procedure with the second group, but with water instead.
These are their results:
Group Increase in pulse rates (beats per minute)
With caffeine 12, 15, 13, 10, 15, 16, 10, 15, 16, 21, 14, 13, 16
Without caffeine 4, 3, 3, 5, 7, 5, 7, 4, 2, 6, 5, 4, 7

a) can you detect any evidence of a systematic error in these results? If so, describe the evidence.
b) can you detect any evidence of a random error in these results? If so, describe the evidence.

Any help will be much appreciated. :D
Update: Results

Group........................Increase in pulse rates (beats per minute)
With caffeine.............12, 15, 13, 10, 15, 16, 10, 15, 16, 21, 14, 13, 16
without caffeine.........4, 3, 3, 5, 7, 5, 7, 4, 2, 6, 5, 4, 7

I figured this is easier to read.
Update 2: Also, can you dumb it down a tad?
2 answers 2