All five of them.
231.57 has five significant figures/numbers. All the numbers in 231.57 are significant.
All nonzero numbers are significant.
Fiirst Class Mail is delivered in three to five days.
Three. All nonzero numbers are significant, and any zeros in between significant numbers are significant.
The figure 18.03 has a total of four significant numbers
Answer: There are six. Answer: There is no such thing as "significant numbers". I assume you mean "significant digits". All digits are significant in this case - a zero (or more than one zero) between other digits is always significant.
Because 10.00400 is 10.004, this has five significant digits (numbers).
1.0348m rounded to 4 significant numbers is 1.035m
They are 4 significant DIGITS, not numbers! It is only 1 number.
All numbers are significant.
The least number of significant figures in any number of the problem determines the number of significant figures in the answer.
3 significant figures.