### Theory:

Most common conversions used in real life:

1. Length:

$$1 \ km = 1000 \ m$$

$$1 \ m = 100 \ cm$$

$$1 \ m = 1000 \ mm$$

$$1 \ cm = 10 \ mm$$

2. Weight:

$$1 \ kg = 1000 \ g$$

$$1 \ g = 1000 \ mg$$

3. Volume (Capacity):

$$1 \ kl = 1000 \ l$$

$$1 \ l = 1000 \ ml$$
Example:
1. Convert $$25.38 \ km$$ to $$m$$.

$$1 \ km = 1000 \ m$$

To convert higher unit to lower unit, we need to multiply by power of $$10$$'s.

$$25.38 \times 1000 = 25380$$

Therefore, $$25.38 \ km = 25380 \ m$$.

2. Convert $$955 \ mg$$ to $$g$$.

To convert lower unit to higher unit, we need to divide by power of $$10$$'s.

$$1 \ g = 1000 \ mg$$

$\frac{1}{1000}$ $$g = 1 \ mg$$

$\frac{955}{1000}$ $$= 0.955$$

Therefore, $$955 \ mg = 0.955 \ g$$.

3. Express $$56 \ ml$$ in $$l$$.

To convert lower unit to higher unit, we need to divide by power of $$10$$'s.

$$1 \ l = 1000 \ ml$$

$\frac{1}{1000}$ $$ml = 1 \ l$$

$\frac{56}{1000}$ $$= 0.056$$

Therefore, $$56 \ ml = 0.056 \ l$$.