A and B are two heavy steel blocks. When B is placed on top of A, the total weight increases by 60%.

• Let the weight of block A be $100x$. When block B is placed on top of block A, the weight increases by 60%.
• Thus, the total weight becomes $100 x + 60\%$ of $100x$, which equals $100x + 60x = 160x$
• Therefore, the weight of block B is $60x$, and the total weight of blocks A and B is $160x$.

When block B is removed from the top, the percentage decrease in weight is calculated as:

• Percentage decrease = $(\frac{60}{160}) \times 100 = 37.5\%$