step 1:

3min -> 2(double)

1hr(60min)-> ?(N) so N (60*2)/3 40

step 2:

N(40)->60min

N/4(10)->?(ans) so ans (60*10)/40 18

the only diff. in the pattern is that time is multiplying by a factor of 3 and the bacteria by a rate of 2. So at 60 th min.. the time multiplication factor is 20 so the bacteria multiplication is N now if we divide both by a factor if 4 it will make 60/4 15 so at the 15th minute the bacteria is N/4.

SK

In 60min its N.so...

60min----N

57 min----n/2(because every 3 min it doubles)

54 min-----N/4

I think u r wrong.

54 is the correct answer.

becoz if at 60 th min it is N then at 57th min it is N/2 and at 54 th min it is n/4