# How many significant figures are in…?

the number 3.90×10^9?

a little description about significant figures would be good too. i haven’t taken chemistry in a while and i just need to brush up on some basics

• MK
1 month ago

Rules for counting significant figures:

1. Nonzero integers always count as significant figures.

2. Zeros that precede all the nonzero digits do not count as significant figures. The number 0.005 has only 1 significant figure.

3. Zeros between nonzero digits always count as significant figures. The number 2.006 has four significant figures.

4. Zeros at the right end of the number are significant only if the number contains a decimal point. The number 100 has only one significant figure, whereas the number 1.00 x 10^2 has three significant figures.

3.90 x 10^9 has three significant figures.

• billrussell42
1 month ago

3

the significant figures are 3, 0.9 and 0.00

Important, note that 3.90 has 3 figures, 3.9 has two. The zero has meaning.

some examples may help

3 figures: 123, 7.51, 7.50, 7.50 e3

2 figures: 120, 7.5, 7.5, 7.5 e3

4 figures: 123.4, 7.510, 7.503, 7.506 e3

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