A vendor bought 9 sweets for rupee 1 at what rate should he sell it to gain 80 percent?

9 sweets for rs:1

therefore CP=1

Gain %=80%

SP=100+gain/100*cp

SP=100+80/100*1

SP=180/100=9/5

therefore 9/5 of 9

=5

threfore he sell 5 sweet for rupee 1