Determine the probability, as a decimal, of randomly choosing a pink or a yellow sweet from the packet.

The volume of the cubic-shaped packet is given as $2744 \text{ cm}^3$.
The formula for the volume of a cube is $\text{Volume} = \text{side} \times \text{side} \times \text{side} = \text{side}^3$.
To find the side length, we need to take the cube root of the volume.

$$\text{side} = \sqrt[3]{\text{Volume}}$$ $$\text{side} = \sqrt[3]{2744 \text{ cm}^3}$$ $$\text{side} = 14 \text{ cm}$$

The side length of the cubic-shaped packet is $\boxed{\text{14 cm}}$.

From Table 2:
Number of pink sweets = 8
Number of yellow sweets = 7
The total number of pink or yellow sweets is the sum of these two values.

$$\text{Number of pink or yellow sweets} = 8 + 7 = 15$$

The problem states there are 35 different coloured sweets in each packet. We can also verify this by summing the numbers in Table 2:

$$\text{Total sweets} = 4 (\text{Blue}) + 5 (\text{Purple}) + 8 (\text{Pink}) + 11 (\text{Orange}) + 7 (\text{Yellow})$$ $$\text{Total sweets} = 35$$

The probability is the ratio of the number of favorable outcomes (pink or yellow sweets) to the total number of possible outcomes (total sweets).

$$P(\text{Pink or Yellow}) = \frac{\text{Number of pink or yellow sweets}}{\text{Total number of sweets}}$$ $$P(\text{Pink or Yellow}) = \frac{15}{35}$$

Simplify the fraction:

$$P(\text{Pink or Yellow}) = \frac{3}{7}$$

Convert the fraction to a decimal:

$$P(\text{Pink or Yellow}) \approx 0.4285714...$$

Rounding to a reasonable number of decimal places (e.g., three decimal places):

$$P(\text{Pink or Yellow}) \approx 0.429$$

The probability of randomly choosing a pink or a yellow sweet is $\boxed{0.429}$.