A submarine can descend from the water surface at the rate of 12 meters per minute after descending for 20 minutes it again rises by 30 meters. what is its new position?
The submarine descends 12 m in a minute. So it will descend 12×20 metres in 20 minutes.
i.e it has descended 240 m.
Now, it has risen 30 metres from that point. So we have to subtract it as it has risen rather than descending.
(If it were descending, then we have to add, otherwise subtract when ascending in this case.)
So, it will be at a height of 240−30=210 metres.
∴ The new position of the submarine is at 210 m from the sea level.