Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 2 - Set Theory - 2.2 Subsets - Exercise Set 2.2: 114

Answer

The set has $7$ elements.

Work Step by Step

A set has $127$ proper subsets. The formula for the number of proper subsets when the set has $n$ elements is: $2^n-1$. $2^n-1=127$ $2^n=128$ $2^n=2^7$ $n=7$ The set has $7$ elements.
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