A tea-packet measures 10 cm × 6 cm × 4 cm.

Dimension of a tea packet is $10 \mathrm{~cm} \times 6 \mathrm{~cm} \times 4 \mathrm{~cm}$.

Volume of a tea packet $=$ length $\times$ breadth $\times$ height $=(10 \times 6 \times 4) \mathrm{cm}^{3}=240 \mathrm{~cm}^{3}$

Also, it is given that the dimension of the cardboard box is $50 \mathrm{~cm} \times 30 \mathrm{~cm} \times 0.2 \mathrm{~m}$, i. e., $50 \mathrm{~cm} \times 30 \mathrm{~cm} \times 20 \mathrm{~cm}$ $(\because 1 \mathrm{~m}=100 \mathrm{~cm})$

Volume of the cardboard box $=$ length $\times$ breadth $\times$ height $=(50 \times 30 \times 20) \mathrm{cm}^{3}=30000 \mathrm{~cm}^{3}$

$\therefore$ The number of tea packets that can be placed inside the cardboard box $=\frac{\text { volume of the box }}{\text { volume of a tea packet }}=\frac{30000 \mathrm{~cm}^{3}}{240 \mathrm{~cm}^{3}}=125$