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Costume 1 · ITWed 9 September1 / 4

Screen resolution

Cancelling a fraction is also how a screen's shape gets its name

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Think about this

A computer screen is 1920 dots across and 1080 down.

We call that screen 16 : 9.

Where did 16 and 9 come from?

1Write down what you think.

Both numbers are divided by the same thing, and the shape does not change. It is exactly the same move as cancelling a fraction.

Now you

2The greatest common divisor of 1920 and 1080 is 120. Do the division and check that you get 16 : 9.

Costume 1 · ITWed 9 September2 / 4

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3An older screen was 1024 by 768, and their GCD is 256. Find the ratio.

4A phone screen is 1170 by 2532, and their GCD is 6. Find the ratio.

5Which of the shapes in questions 2 and 3 is wider? Answer from the ratio alone, and say how you can tell.

16 : 9 and 4 : 3. Try dividing the width by the height.

6A 4K screen is 3840 by 2160. Is that the same shape as 1920 by 1080? Cancel it down and check.

Costume 1 · ITWed 9 September3 / 4

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7A photo is 6000 by 4000. Write the ratio in its simplest form.

8A screen is 1280 by 720 and their GCD is 80. Find the ratio.

9A screen is 2048 by 1536 and their GCD is 512. Find the ratio.

10On a 16 : 9 screen the height is 1440. How wide is it?

Costume 1 · ITWed 9 September4 / 4

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11Which is the wider shape, a 4 : 3 photo or a 16 : 9 screen? Say why.

12Is putting a ratio in its simplest form the same thing as cancelling a fraction, or different? Explain in words.

Set today's ratios beside Friday's cancelling.

Extra · you may skip this

On a 16 : 9 screen, if the width is 2560 dots, what is the height?