Question

tap a can fill a cistern (tank) in 1 hour 30 minutes and tap b can fill in 1 hour in how many minutes will the cistern be filled up if the both the taps are opened at a time

Answer 1

work done by tap a in 1 min=1/90min
work done by tap b in 1 min=1/60min
work done by both taps =1/90+1/60min=1/36min
=36 min

Answer 2

1hour =60 min
therefore 1hour 30minut =60+30=90 min

1\90+1\60
=2+3\180
=5÷180
=1\36
both will do whole part of work
=1÷1\36
=1×36\1
=36
both will fill cestern only 36 minutes