When we convert a larger unit (m) to a smaller unit (cm), we multiply by the conversion factor.

Therefore, to convert length given in metres (m) to centimetres (cm) we have to multiply by 100.

Capacity of 5 glasses = 2 Litres

When we convert a larger unit (L) to a smaller unit (mL) we multiply.

1 Litre = 1000 mL
Hence 2 Litres = 2 $\times$ 1000 = 2000 mL
Capacity of 1 glass = Total capacity $÷$ No. of glasses

Capacity of 1 glass = 2000 $÷$ 5
                                = 400 mL

We know that 1 kg = 1000 g

Therefore, 300 g + ______ = 1000 g

= 1000 g - 300 g

= 700 g

String `A` is starting from 1 cm.
$\therefore$ Subtract 1 cm from 9 cm.
Lenght of string A
$=9cm-1cm=8cm$
String `B` is starting from 3 cm.
$\therefore$ Subtract 3 cm from 10 cm.
Length of string B
$=10cm-3cm=7cm$
Thus, the difference in length of  String `A` and String `B`
$=8cm-7cm=1cm=10mm$
$\therefore$ The length of string A is more than string B by 10 mm.

$\text{Weight of mangoes + 100 g + 500 g}=\text{1 kg + 2 kg}$
$\Rightarrow \text{Required weight + 600 g}=\text{3 kg}$
$\Rightarrow \text{Required weight}=\text{3 kg - 600 g}$
To move ahead, we need to convert the units. Since we need the final answer in kilograms, let us convert 600 g to kilograms.
        $1\text{kg}=1000\text{g}$
$\Rightarrow \text{600 g}=\frac{600}{1000}\text{kg}$
                $=0.6\text{kg}$
$\therefore \text{Weight of mangoes}=\text{3 kg - 0.6 kg}$
                                        $=\text{2.4 kg}$

We know that,
1 m = 100 cm
1 km = 1000 m
1 cm = 10 mm
$\therefore$ In the 4 given options, 1 m = 100 cm is correct.

Kilogram (kg) and milligram (mg) are the units of mass.

Millimetre (mm) is the unit used to measure the length of very small objects like the length of a pin, seed etc. 

Kilometre (km) is the unit used to measure long distances between two places.

     $1\text{L}=1000\text{mL}$
$\Rightarrow 3\text{L}=3\times 1000\text{mL}$
            $=3000\text{mL}$
Therefore, the quantity of juice Tina wants to buy equals 3000 mL.
Since the store sells only 250 mL cartons, the number of such cartons that Tina has to buy is given by $\frac{3000}{250}=12.$

Both the quantities 4 kg and 400 g have different units.

So let's convert 4 kg to grams.

We know that 1 kg = 1000 g
(To convert a larger unit (kg) to a smaller unit (g) we multiply by the conversion factor.)

Therefore, 4 kg = 4 $\times$ 1000 g

Now, 4000 g - 400 g = 3600 g

     $1\text{L}=1000\text{mL}$
$\Rightarrow 6\text{L}=6\times 1000\text{mL}=6000\text{mL}$
Thus, the total quantity of lemonade to be prepared is 6000 mL. The quantity of lime juice that we have is 3800 mL.

$\Rightarrow$ Quantity of water required to make the lemonade is given by
6000 mL - 3800 mL = 2200 mL.