A sells a phone to B at 50 percent profit. Then B sells back it to A at 40 percent loss. Now A sells it to C at a gain of 30 percent. What is the overall gain percent of A?? Please answer this question

40.5%?

Non of the faculty has commented.

Suppose A has bought the phone for Rs.1000
he then sold it to B for 50% profit which is Rs 1500
Then, B sold it back to A for 40% loss which is Rs 900
then, Again A sold it to C for 30% profit which is Rs 1170
Now for your clear understanding you can treat this question as: A has 2 items
for 1st item the CP is 1000 and SP is 1500
for 2nd item the CP is 900 and SP is 1170
now apply profit formula
(total profit/total CP)* 100
which is
profit:600+270=870
and Total CP is 1000+900=1900
(870/1900)*100
=45.7%

80 is correct answer