A coil takes $15\,\min$ to boil a certain amount of water, another coil takes $20\,\min$ for the same process. Time taken to boil the same amount of water when both coil are connected in series ........... $min$
A$5$
B$8.6$
C$35$
D$30$
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C$35$
c (c) Time ${t_S} = {t_1} + {t_2} = 35\,\,\min .$
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