How do we calculate bandwidth from signal formula?

How can we calculate the bandwidth of distinct signals like this? I guess the right answer is 90 - 10 = 80 Hz. But I have a hard time understanding why is this calculated in that way. I thought the bandwidth is calculated by the diversity of signals and since there aren't in-between frequencies like 11, 12... in the image there are 5 signals, shouldn't the bandwidth be 5 Hz? What am I missing here?

• To answer this question, first you need to define "bandwidth". There are many definitions, and each gives a different answer.
– MBaz
Commented Dec 5, 2020 at 17:09
• I only used Herz as bandwidth in my question so I thought it would be clear that I am asking about bandwidth as Herz @MBaz
– Abcd
Commented Dec 5, 2020 at 19:02
• I don’t think the units were in question. The point is that bandwidth could have different definitions based on context. What are you doing with it, or do you have a preferred definition which could be used to answer the question? Commented Dec 5, 2020 at 19:36
• What @DanSzabo said: bandwidth is always measured in Hz, but there are many ways to measure it.
– MBaz
Commented Dec 5, 2020 at 20:45