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primary 6 | Maths
| Percentage
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Date Posted: 4 years ago
Views: 361
There is no change in the number of red pens, but somehow because 15 green pens are removed, the percentage of red pens increases from 60% to 80%.
Old ratio of green : red is 40 : 60, or 2 : 3.
New ratio of green : red is 20 : 80, or 1 : 4.
But then, because the actual number of red pens is unchanged, we must make the “3” and “4” in our ratios the same.
We rewrite 2 : 3 as 8 : 12 and 1 : 4 as 3 : 12.
This means that there are 12 units of red pens and there is a decrease in the number of green pens from 8 units to 3 units.
So, 5 units = 15 pens
1 unit = 3 pens
In total, there are 20 units of pens at first, or 20 x 3 = 60 pens at first (consisting of 24 green pens and 36 red pens at first).
Old ratio of green : red is 40 : 60, or 2 : 3.
New ratio of green : red is 20 : 80, or 1 : 4.
But then, because the actual number of red pens is unchanged, we must make the “3” and “4” in our ratios the same.
We rewrite 2 : 3 as 8 : 12 and 1 : 4 as 3 : 12.
This means that there are 12 units of red pens and there is a decrease in the number of green pens from 8 units to 3 units.
So, 5 units = 15 pens
1 unit = 3 pens
In total, there are 20 units of pens at first, or 20 x 3 = 60 pens at first (consisting of 24 green pens and 36 red pens at first).
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done
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As Mr Eric said, this uses ‘one side unchanged’.
Date Posted:
4 years ago
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