12 apples weigh 2 kg 500 g. How many apples will weigh 15 kg?

First, convert weight to a single unit:

1000 g = 1 kg

500 g = 0.5 kg

∴ 2 kg 500 g = (2 + 0.5) kg = 2.5 kg.

For 2.5 kg, number of apples = 12.

For 1 kg, number of apples = $\Big(\dfrac{12}{2.5}\Big)$. $\quad$[Less weight, Less apples]

Multiply by 10 to remove decimals.

For 1 kg, number of apples = $\Big(\dfrac{12 \times 10}{2.5 \times 10}\Big) = \Big(\dfrac{120}{25}\Big)$ apples

For 15 kg, number of apples = $\Big(\dfrac{120}{25} \times 15\Big) \text{ apples} \quad \text{[More weight, More apples]}$

= $\Big(\dfrac{120}{5} \times 3\Big) \text{ apples} \quad \text{(Dividing 15 and 25 by 5)}$

= 24 x 3 apples $\quad$ (Dividing 120 and 5 by 5)

= 72 apples.

Hence, 72 apples will weigh 15 kg.