Question

Is this correct?
histograms

Answer 1

I agree.

{1.3} forms the first bar on the interval 1-3 (height 2)
{4,4,5,5,6} forms the second bar on the interval 4-6(height 5)
{7,8,9} forms the third bar on the interval 7-9(height 3)
{10} forms the last bar on the interval 10-12 (height 1)

Answer 2

Thanks