The midpoint of the interval whose boundaries are 27.5 and 38.5 is

33

Step-by-step explanation:

Sounds as tho' you're working with a number line.  On this line you have 27.5 and 38.5 marked, and your task is to determine the midpoint.  To do this, find the average of 27.5 and 38.5:

27.5 + 38.5      66

= 33.  The desired midpoint is 33.

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Step-by-step explanation:

Universal Set. Simple