Significant figures & errors of measurement complete the following with “are” or “are not: 1. zeros between two significant digits significant. 2. zeros to the right of a decimal point that precede all nonzero digits significant. 3. all nonzero digits significant. 4. one or more final zeros used after the decimal point significant. 5. zeros used solely for spacing the decimal point significant. determine the number of significant figures in each of the following numbers: 1. 5.432 2. 40.319 3. 146 4. 3.285 5. 0.189 6. 249.3 7. 2873.0 8. 99.9 9. 0.000235 10. 144 11. 2500 12. 2500.0 13. 1.04 14. 3.58 15. 48.57193 16. 8365.6 17. 0.002300 18. 7.500 19. 3.92 20. 1.00

1. Zeros between two significant digits ARE significant.  e.g.  in the number 809, the 0 is significant to the value of the number 

2. Zeros to the right of a decimal point that precedes all nonzero digits ARE significant.  e.g. in 0.0674, the 0 that comes after the decimal point is important to the overall value of the other digits.

3. All nonzero digits ARE significant.  (Nonzero digits are ALWAYS significant)

4. One or more final zeros used after the decimal point ARE significant. e.g. in the number 35.00 the zeros indicates the possibility of further digits beyond the zeros and as such make then significant

5. Zeros used solely for spacing the decimal point ARE NOT significant.
e.g. in the number 0.46, the zero has no bearing on the .46 thus not adding value to the number. 

Determine the number of significant figures in each of the following numbers:
 
I highlighted those digits that are significant and put the number of sig. fig. in brackets

1)  5.432  (4 sig. fig.)

2)  40.319 (5 sig. fig.)

3)  146  (3 sig. fig.)

4)  3.285  (4 sig. fig.)

5)  0.189 (3 sig. fig.)

6)  249.3 (4 sig. fig.)

7)  2873.0 (4 sig. fig.)

8)   99.9 (3 sig. fig.)

9)  0.000235 (6 sig. fig.)

10)   144 (3 sig. fig.)

11)  2500 (2 sig. fig.)

12)  2500.0 (5 sig fig) -  the decimal point makes the zeros that precede it signicficant

13)  1.04 (3 sig fig)

14)  3.58  (3 sig fig)

15)  48.57193 (7 sig fig)

16)  8365.6 (5 sig fig)

17)  0.002300 (4 sig fig)

18) 7.500 (2 sig fig)

19) 3.92  (3 sig fig)

20) 1.00 (3 sig fig)

Ithink ahopefully im correct 

Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.