Video: AQA GCSE Mathematics Foundation Tier Pack 2 • Paper 2 • Question 16

Some children are playing a board game and have placed some pieces on a board. There are 35 red dragons, 41 green dragons, and 185 trolls on the board. 21 dragons are removed from the board. The red dragons now make up 12.5% of the total number of pieces on the board. How many green dragons are left on the board?

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Video Transcript

Some children are playing a board game and have placed some pieces on a board. There are 35 red dragons, 41 green dragons, and 185 trolls on the board. 21 dragons are removed from the board. The red dragons now make up 12.5 percent of the total number of pieces on the board. How many green dragons are left on the board?

The first thing we need to calculate is the total number of initial pieces on the board, which will be the 35 red dragons plus the 41 green dragons plus 185 trolls. And so we start the game with 261 pieces on the board.

To calculate how many pieces are remaining on the board, we take the starting 261 and we subtract the number of dragons that were removed. 261 minus 21 equals 240. At this point, there are 240 pieces on the board. And 12 and a half of the total number of pieces on the board now are red dragons, that is, 12 and a half percent, 12.5 percent, of the final number of pieces, 240.

To find 12 and a half percent of 240, we can write 12 and a half percent as 12.5 over 100 and multiply that by 240. We can also write this 12 and a half out of 100 as 0.125. Both of these values are equivalent. So either way, you multiply them by 240 and you get 30.

Remember, this 12 and a half percent tells us the number of red dragons that are still on the board. But we need to know how many green dragons are left on the board. We now need to calculate how many red dragons were removed. We started with 35 red dragons, and we ended with 30 red dragons on the board. 35 minus 30 equals five. Five red dragons were removed.

We know that a total of 21 dragons were removed from the board. If we subtract the five dragons that were red from this amount, we get 16. This tells us that 16 green dragons were removed. We started with 41 green dragons. 16 of them were removed. 41 minus 16 equals 25. There were 25 remaining green dragons on the board.

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