Problem of the Week-10/1/2010

Problem of the Week – 10/1/2010

Certain digits appear the same when reflected across horizontal lines or vertical lines. This week’s problem:  which two-digit numerals appear the same when reflected across a horizontal line? Which two-digit numerals appear the same when reflected across a vertical line? To answer, provide the list for the horizontal line and the list for the vertical line.

Send your answers as comments to this blog post. You need not worry about incorrect answers being posted. I will post only those answers that are correct, and I will post the first five correct answers on Monday.

Feel free to share this problem with anyone who might like to try it.

Reflection of a triangle about the y axis

Reflection across the y-axis

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3 Responses to “Problem of the Week-10/1/2010”

  1. Sharron Herring says:

    The answer to this question depends on your penmanship style or type font. The only digits that have any hope at all of reflecting are 0, 1, and 8. The 1 can only do so if written as a straight line with no slant and no embellishments. For the 8, if the top section is narrower than the bottom it only reflects horizontally, but it can reflect both ways if the top and bottom are printed equally, and again without slant. The 0, without slant, can reflect both ways. Another consideration is size. As I type this, it appears the 0 and 1 are the height of the lower case letters, but the 8 is the height of the tall letters. If a short and tall digit were reflected horizontally, the short one would sit on the ground in the upper part of the picture, and it would seem to float in the air in the lower part.

    With all letters the same height and with no embellishments or slants, the following two-digit numbers may reflect horizontally: 11, 88. Because oo has no meaning over just a 0 alone, I’m not counting it.

    With the above restrictions on form, these two-digit numbers may reflect vertically: 10, 11, 18, 80, 81, 88

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  2. Sharron Herring says:

    Corrections to my earlier post:
    2nd paragraph: With all the “numbers” the same height.
    2nd and 3rd paragraphs: two-digit “numerals”

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  3. Eric B says:

    If you use block numbers (think digital clock)

    Across a horizontal line: 10, 11, 18, 30, 31, 33, 80, 81, 88

    Across a vertical line: 11, 25, 52, 88

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