Ahistogram is being made for the following list of data.
78, 92, 98, 87, 86, 72, 92, 81, 86, 92
if the length of each interval is going to be 6, what will be the frequency of the first interval?
a. 1
b.2
c.3
d.4

Altho' you don't strictly have to, you might want to rearrange this data in increasing order.

next, let's look at a possible horiz. axis that accommodates all of the given data.   the smallest data point is 72.   you could begin the first interval with 72.   adding 6 would give you 78.   generally, you'd assume that you count the elements that are   72 or greater, but you do not include the 78 at the end of the interval.   thus, the first interval would be [72,78), which includes 72 but not 78.   so, the frequency in the first interval would be 1, reflecting the first data point, 72.