If the CPI declined from 400 in 1998 to 350 in 1999,by what percentage did the price level decline?

CPI

Measuring the average price for a set basket of goods and services consumed by people, from food to healthcare and transportation, the Consumer Price Index employs their weighted average prices for assessment.

Price Level

The average of current prices across the entire spectrum of goods and services produced in the economy, often measured by inflation indicators.