Given :
In the early spring, the trout at Big Blue Lake swim at a depth of 30 feet below sea level.
When the lake warms up in the summer, the trout swim 20 feet deeper than that , d = 20 feet .
To Find :
At what position relative to sea level do the trout swim in the summer.
Solution :
Depth in spring from surface , [tex]D_s=30\ feet[/tex] .
Let , depth in summer is D .
Now , depth in summer relative to sea-level is :
[tex]D=D_s+d\\\\D=30+20\ feet\\\\D=50\ feet[/tex]
Therefore , trout swim 50 feet deep below the sea level in the summer .
Hence , this is the required solution .
