Since 450 liters represents 45%, then each 1% is equal to 450 liters/45 = <<450/45=10>>10 liters.

Hence, the capacity of each tank is 10 liters x 100 = <<10*100=1000>>1000 liters.

So, the first tank needs 1000 - 300 = <<1000-300=700>>700 liters of water more.

While the second tank needs 1000 - 450 = <<1000-450=550>>550 liters more.

Therefore, 700 + 550 = <<700+550=1250>>1250 liters of water are needed to fill the two tanks.

# Answer

1250
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
The first tank is 300 liters filled while the second tank is 450 liters filled. The second tank is only 45% filled. If the two tanks have the same capacity, how many more liters of water are needed to fill the two tanks?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
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user
1250
The first tank is 300 liters filled while the second tank is 450 liters filled. The second tank is only 45% filled. If the two tanks have the same capacity, how many more liters of water are needed to fill the two tanks?
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