A student says: 'The Earth pulls a 3 kg stone twice as hard as a 1.5 kg stone, so the heavy stone…

Step 1. The pulls. $3\ \text{kg} \times 9.8\ \text{m/s}^2 = 29.4\ \text{N}$ and $1.5\ \text{kg} \times 9.8\ \text{m/s}^2 = 14.7\ \text{N}$: the student is right about these.

Step 2. The accelerations. $\dfrac{29.4\ \text{N}}{3\ \text{kg}} = 9.8\ \text{m/s}^2$ and $\dfrac{14.7\ \text{N}}{1.5\ \text{kg}} = 9.8\ \text{m/s}^2$.