Using proportions, it is found that the children made 408 snowflakes on the third day.
What is a proportion?
A proportion is a fraction of a total amount, and the measures are related using a rule of three.
On the first day, they made 30% of the total amount of 1,200, hence:
D1 = 0.3 x 1200 = 360
On the second day, they made 20% more day in the first, hence:
D2 = 1.2 x 360 = 432.
On the third day, they made the remaining amount, hence:
D3 = 1200 - (360 + 432) = 408.
More can be learned about proportions at https://brainly.com/question/24372153
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