Block volume decreases 3.2% when x increases 10% and y decreases 20%.
Let's say the original dimensions of the block are x = 10 cm and y = 10 cm. Then, the original volume of the block is
V₁ = x²y = 10² * 10 = 1000 cm³.
When x increases by 10%, it becomes x = 10 * 1.1 = 11 cm. And, when y decreases by 20%, it becomes y = 10 * 0.8 = 8 cm.
So, the new volume of the block is V₂ = x²y = 11² * 8 = 968 cm³.
The percentage change in volume is calculated as:
((V₂ - V₁) / V₁) * 100%
Plugging in the values:
((968 cm³ - 1000 cm³) / 1000 cm³) * 100% = -3.2%
Therefore, the volume of the block decreases by 3.2% when x increases by 10% and y decreases by 20%.