Answer the questions based on the information given below:
Purana and Naya are two brands of kitchen mixer-grinders available in the local market. Purana was an old brand that was introduced in $1990,$ while Naya was introduced in $1997.$ For both these brands, $20\%$ of the mixer grinders bought in a particular year are disposed of as junk exactly two years later. It is known that $10$ Purana mixer-grinders were disposed off in $1997.$ The following figure shows the number of Purana and Naya mixer-grinders in operation from $1995$ to $2000,$ as at the end of the year.
How many Naya mixer-grinders were purchased in $1999?$
- $45$
- $50$
- $55$
- $64$