# Which has an infinite number of significant figures

I have a chem final on Tuesday and I am really really lost....

anyways...I really don't understand this question:

Which of the following has an infinite numer of significant digit?

A. 100.m  B. 12 apple/doz  C. 90km/h  D. 5.6b/ml
HOW CAN SOMETHING HAVE A INFINITE SIG FIG??!! I DON"T GET IT... ???
PLZ HELP... :'(

Exact numbers have an infinite number of significant figures.

Exact numbers are one of two categories,

counting numbers: 12 cars, 5 molecules, 10 books, etc

definitions:  1mm = .001 m; 12 in = 1ft, etc

thank you very much~ ;D

Hello,
The significant figures are those digits that cary meaning contributing to its accuracy. Its concept is usually used in connection with rounding. Still u need to follow certain rules for identifying significant digits....
1. All non zero digits are considered significant. like 234.67 has five significant figures: 2 , 3, 4, 6, and 7.
zeros appearing anywhere between two non-zero digits are significant. like 101.12.
leading zeros are not significant. example..... 0.00018 would have only two significant figures.....1 and 8.
trailing zeros in a number containing a decimal point are significant. The significance of trailing zeros in a number not containing a decimal point can be ambiguous.
A number with all zeros has no significant digits...because the uncertainity is larger than actual measurement.  example.....0.0000

I hope that helps.