1. The intensity decreases as the square of the distance, so increasing the distance by a factor of 10 decreases the intensity by a factor of 10 x 10 = 100.

2. The intensity varies as the square of the distance, so the apparent intensity will increase by (100 / 60 ) ² = 2.78.

3. ( R ₁ / R ₂ ) ² = 10; thus, R ₁ / R ₂ = 10 ^{1 / 2} = 3.16