A 5-metre board has 1.85 metres cut away. Enter the remaining length in metres.

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Writing 5 as 5.00 and subtracting gives 5.00 - 1.85 = 3.15 metres. Subtracting the digits without aligning decimal places can produce 4.15, which incorrectly treats 0.85 as only 0. The wrong answer 4.15 equals 5.00 minus 0.85: it subtracts only the 0.85 and ignores the whole dollar in 1.85.