How many significant figures in a) 400 b) 400g?

Question

Give reason also

Answer 1

In both cases, inthe way you've stated the question, 1 significant figure.

Rules are:
1) zero's within a number are significant e.g. 404 has 3 significant figures
2) zero's after a decimal point are significant e.g. 4.00 has 3 signifcant figures
3) Other trailing zero's are NOT significant. e.g. 400 or 4000 or 400000 have 1 significant figure.

The only exception I would make is if the number is a result of an equation that had more significant figures. e.g. if you knew the derivation of your answer was from say: 16 x 25 = 400 then I'd say the answer has 2 significant figures.

Answer 2

The number of significant figures in a measurement, such as 2.531, is equal to the number of digits that are known with some degree of confidence (2, 5, and 3) plus the last digit (1), which is an estimate or approximation. As we improve the sensitivity of the equipment used to make a measurement, the number of significant figures increases.
Zeros within a number are always significant. But Zeros that do nothing but set the decimal point are not significant. Both 400 and 400g contain one significant figures.
Trailing zeros that aren't needed to hold the decimal point are significant. For example, 4.00 has three significant figures.

If you are not sure whether a digit is significant, assume that it isn't. For example, if the directions for an experiment read: "Add the sample to 400 ml of water," assume the volume of water is known to one significant figure.

Answer 3

The simple answer is that you can not tell out of context.
If you have "there are about 400 ballons" it is 1 sig fig.
If you have "we measured exactly 400 ballons" it is 3 sig figs.

Same thing with the 400g, it could be 1, 2, or 3. Was it weighed on a balance that gave one, two, or three places (one,tens,hundreds) or estimates by eyeball? It is always a good idea not to use such percise numbers. 401 makes it much easier.

Answer 4

This is a trick question : significant figures apply ONLY to measured quantities. Therefore, in a) the question about significant figures is not relevant. In b) there is only one significant figure. To indicate 3 sig. fig. it should have been written as 400. g (note the decimal point after the second zero). To indicate 2 sig. figures, the situation becomes somewhat complicated where the notation needs to be converted to Standard Form, to give 4.0 x10^2 g

Answer 5

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