How can we find No of significant figures | How a number can be rounded off

Описание: Here are the rules to find the number of significant figures in any measurement or number. I’ll keep them clear and simple:


---

✅ Rules for Significant Figures

1. All non-zero digits are significant.

Example:

345 → 3 significant figures

7.89 → 3 significant figures




---

2. Zeros between non-zero digits are significant.

Example:

205 → 3 significant figures

1002 → 4 significant figures




---

3. Leading zeros (zeros before the first non-zero digit) are not significant.

They only show the position of the decimal.

Example:

0.03 → 1 significant figure

0.00452 → 3 significant figures




---

4. Trailing zeros (zeros at the end) are significant only if there is a decimal point.

Example:

50.0 → 3 significant figures

2.300 → 4 significant figures




---

5. Trailing zeros in whole numbers without a decimal point are NOT significant (unless stated).

Example:

1500 → 2 significant figures

70000 → 1 significant figure



(Unless written in scientific notation to make them clear.)


---

**6. Exact numbers (counted items or defined constants) have infinite significant

Here are the rules for rounding off numbers (commonly used in math, physics, and chemistry). I’ll explain them clearly:

✅ Rules for Rounding Off

1. Identify the rounding place

Decide which digit you are rounding to:

nearest whole number, tenth, hundredth, significant figure, etc.

2. Look at the digit after the rounding place

This digit determines whether you round up or stay the same.

✔️ If the next digit is 0, 1, 2, 3, or 4 → ROUND DOWN

Leave the rounding digit unchanged.

Drop all digits after it.

Example:
3.142 → rounded to 3 significant figures = 3.14

✔️ If the next digit is 5, 6, 7, 8, or 9 → ROUND UP

Increase the rounding digit by 1.

Drop all digits after it.

Example:
5.678 → rounded to 3 significant figures = 5.68

3. Special rule for 5 (when exactly 5)

Sometimes called “round half up” (the most common rule in school):

✔️ If the next digit is 5, you round up.

Example:
4.25 → rounded to 2 d.p. = 4.3

4. If rounding creates a carry-over

If rounding up makes a digit exceed 9, carry to the next place.

Example:
9.96 (round to 2 significant figures)
→ 10.0 (3 significant figures)
→ 10 (2 significant figures)

5. For whole numbers, zeros added after rounding may or may not be significant

Example:

Round 2486 to 2 significant figures → 2500
(Only “25” are significant unless a decimal point is shown.)

6. For decimal numbers, zeros at the end after a decimal are significant

Example:

Round 2.348 to 3 significant figures → 2.35

#significantfigure #roundoff