Let x be the month on which the fee for two plans are equal.
Therefore,
150 + 10x = 50 + 30x
10x - 30x = 50 - 150
-20x = -100
x = 5
Cumulative cost = 150 + 10(5)
= 150 + 50
= 200
Hence, Karan will pay a cumulative cost of $200 dollars with either plan to go to the gym for 5 months.