# Chemistry Help. Subtract 7.15 cm from 9.0 cm?

How many cm

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• Anonymous
8 years ago

1.85 cm to a mathmatician

however since 9.0 has two significant digits to a chemist 1.9 cm

Source(s): Soc
• First do the math, 9.0 - 7.15 = 1.85 Now if you are a mathematician, you are through. If you are a scientist you know that dealing with measurements, you have to use what we call significant figures. These rules for sig figs let us know the limits of the measurements. For multiplication and division, the answer can have no more sig figs than the least of the starting numbers, but when we get to adding and subtracting, we have to look at places past the decimal and the answer can only have the same number of places past the decimal as the least of the starting numbers. Now 9.0 has only one place past the decimal, so we have to limit ourselves to one place in the answer. Now, do we round off 1.85 to 1.8 or 1.9? When I went to school, the rule was that if the digit to be dropped was a 5 and the number before it was even, leave it alone, but if the number before it was odd, raise it - so according to what I think of as old school, the answer would be 1.8 However most modern texts I have taught out of say that if the number to be dropped is 1-4, leave the previous number alone but if the number to be dropped is 5-9, raise the previous number. This would give us 1.9 which I think most modern text books would agree with. Sorry to be long winded, but you did ask :-)

Source(s): Teaching this stuff every semester.
• Anonymous
8 years ago

1.85cm

• Anonymous
8 years ago

1.85cm