Assume that a market basket of goods costs $900 in 2018. That same market basket costs $950 in 2019. In 2020, that same market basket of goods costs $800. If we use 2018 as the base year, what is the...

Assume that a market basket of goods costs $900 in 2018.  That same market basket costs $950 in 2019.  In 2020, that same market basket of goods costs $800.  If we use 2018 as the base year, what is the price index in 2020?