Question

a motorboat cover 20 km in 4 hours what distance will it cover in 7 hours

Answer 1

in 4 hrs he covers=20km
----1--------------------=20/4=5km
----7--------------------=5×7=35km

Answer 2

$distance \: covered \: by \: motorboat \: in \: 4 \: hr = 20km \\ \\ distance \: covered \: by \: motorboat \: in \: 1 \: hr = \frac{20}{4} = 5 \: km \\ \\ so \\ distance \: covered \: by \: motorboat \: in \: 7 \: hr = 7 \times 5 = 35 \: km$