Assumings both at their thresholds
Sue swimming at 1.3m/s and Mary at 1.5 Ms
In 2 min headstart sue would cover 120*1.3m=156m.
Now assume sue stops there and Mary goes on at the realtive speed of 0.2 m/s ... Mary needs 156*5 =780seconds to go ahead of sue...
At less. Than 75/78 m/s Mary can overtake... At more than (75/78)m/s she can not...
So Sue going at less than 1.3 is not a Good indicator to give a unique answer
Hence E
Sue swimming at 1.3m/s and Mary at 1.5 Ms
In 2 min headstart sue would cover 120*1.3m=156m.
Now assume sue stops there and Mary goes on at the realtive speed of 0.2 m/s ... Mary needs 156*5 =780seconds to go ahead of sue...
At less. Than 75/78 m/s Mary can overtake... At more than (75/78)m/s she can not...
So Sue going at less than 1.3 is not a Good indicator to give a unique answer
Hence E
