Answer:
increased by 10%
Explanation:
When we consider that nominal value of worker's wage has increased in 10 years the means his purchasing power has increased by 50%. He can purchase more with his wages.
But also it was stated that prices also went up 40% during this period. This can be as a result of inflation, resulting in reduced purchasing power.
The net increase in purchasing power of the worker = Increase in wages - Increase in prices
= 50-40= $10