Fill in the blanks: (a) 1 year = months, (c) 365 days = year, (e) 1 litre = ml, (g) Half of 80 = .

$$1 \text{ year} = 12 \text{ months}$$

The blank is 12.

b)

$$1 \text{ week} = 7 \text{ days}$$

The blank is 7.

c)

$$365 \text{ days} = 1 \text{ year}$$

The blank is 1.

d)

$$1 \text{ meter} = 100 \text{ cm}$$

The blank is 100.

e)

$$1 \text{ litre} = 1000 \text{ ml}$$

The blank is 1000.

f)

$$1 \text{ km} = 1000 \text{ m}$$

The blank is 1000.

g)

$$\frac{1}{2} \times 80 = 40$$

The blank is 40.

h)

$$\frac{1}{3} \times 90 = 30$$

The blank is 30.

Here are the final answers:

a) 1 year = $\boxed{\text{12}}$ months

b) 1 week = $\boxed{\text{7}}$ days

c) 365 days = $\boxed{\text{1}}$ year

d) 1 meter = $\boxed{\text{100}}$ cm

e) 1 litre = $\boxed{\text{1000}}$ ml

f) 1 km = $\boxed{\text{1000}}$ m

g) Half of 80 = $\boxed{\text{40}}$

h) One-third of 90 = $\boxed{\text{30}}$