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Thought for the day: Sometimes a Creative Math Prompt may encourage you to pay closer attention to something you have seen many times.

Concepts: length and area; fractions; ratios; percentages

 
 

Examples of noticing and wondering

I notice that only one (area) measurement is given on the flag.
I notice that the areas of the three other red rectangles and three of the white rectangles are the same as the given area.
I notice that the given area looks to be a little greater than half of the area of each longer red or white stripe.
I notice that the vertical length of the blue rectangle is 7 times the vertical length of each stripe.
I notice  that the 50 stars are arranged in alternating rows of five and six stars.

I wonder what fraction of the width of the flag the small stripes are.
I wonder if the flag is drawn to scale.
I wonder if it is possible to determine all of the length and area measurements of the flag just by looking at the picture.
I wonder what the width : length ratio is for the flag.
I wonder how much fabric it would take to make the whole flag (and how much of each color).
I wonder what the length and width of the flag are.

 
 

Notes

You can find a more structured problem built around this image in in Exploration 4: Perplexing Percentages from my book, Advanced Common Core Math Explorations: Ratios, Proportions, and Similarity.

Students may make measurements of the picture to determine ratios of different lengths. A key fact is that the (horizontal) width of the blue rectangle is 2/5 or 40% of the width of the entire flag. Also, the width : length ratio for the flag is 1.9. (Ratios of the flag dimensions vary somewhat [from about 1.6 to 2], but 1.9 is typical, and it applies to this picture.)

Given this information, students can calculate all of the relevant lengths and areas except for those of the stars. They can also determine percentages or other ratios relating these measurements. Calculating or estimating the areas of the stars would be an interesting challenge. Some students may also be curious about the scale factor between the picture and the actual flag that it represents.

A few sample results:

  • The red stripes cover about 41.5% of the total area of the flag.
  • The red stripes cover an area of 19.8 square feet.
  • The white stripes cover about 36.9% of the total area of the flag.
  • The white stripes cover an area of 17.6 square feet.
  • The total area of the flag is 47 and 2/3 square feet.
  • The vertical length of the flag is very close to 5 feet (about 5.01).
  • The horizontal length of the flag is very close to 9.5 feet (about 9.52).

Some students may enjoy doing similar investigations for other flags, especially if they have another country of origin or if they special connections to other countries.

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