Math Problem Statement

Halina’s clock uses a digital LED display where each digit is represented by seven LED segments that are either on or off, as shown. Sometimes some of the LED segments stop working. When the top- most horizontal LED segment stopped working, both the digit 1 and the digit 7 appeared as shown. This was a problem because Halina couldn’t distinguish between them. Halina replaced the broken LED segment, but then a week later found that a different LED segment had stopped working. However, this time, she was still able to distinguish between all ten digits. What is the largest number of LED segments that can be broken at the same time, while still allowing Halina to distinguish between all ten digits?

Solution

The problem asks for the largest number of LED segments that can be broken simultaneously, while still allowing Halina to distinguish between all ten digits on a seven-segment digital display. Let's walk through the reasoning.

1. Understanding the seven-segment display:

Each digit in a seven-segment display is represented by a combination of segments that can either be on or off. The seven segments are typically labeled as follows:

 a
 ---
f |   | b
  | g |
 ---
e |   | c
  |   |
 ---
 d

The segments a,b,c,d,e,f,ga, b, c, d, e, f, g can be turned on or off to form digits 0 through 9. The table below shows the segment configuration for each digit:

Digitabcdefg
01111110
10110000
21101101
31111001
40110011
51011011
61011111
71110000
81111111
91111011

Here, a 1 means the segment is on, and a 0 means the segment is off.

2. Identifying Distinguishability:

The goal is to determine the largest number of segments that can break, while still allowing all 10 digits to be distinguishable. For two digits to be distinguishable, the pattern of "on" and "off" segments for each digit must remain unique.

If too many segments are broken, the remaining segments might show identical patterns for multiple digits, making them indistinguishable. Therefore, we want to maximize the number of broken segments, while ensuring no two digits appear the same.

3. Strategy for Breaking Segments:

To maximize the number of broken segments, we need to carefully choose which segments can be broken without causing ambiguity. We aim to maintain enough distinct patterns to represent each digit uniquely.

After analyzing the segment configurations, it turns out that three specific segments can be broken while still maintaining distinguishable digits. These segments are:

  • Segment ee
  • Segment

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Math Problem Analysis

Mathematical Concepts

Combinatorics
Logic
Digital Displays

Formulas

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Theorems

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Suitable Grade Level

Grades 9-12