Given :
One afternoon she dove -7.8 feet.
Her next two dives were each 2 1/8 feet deeper than the dive before it.
To Find :
The depths of her second and third dives.
Solution :
Depth of her second dive,
[tex]d_2=-(7.8+2\dfrac{1}{8})\\\\d_2=-(7.8 + \dfrac{17}{8})\\\\d_2 = -9.925\ feet[/tex]
Depth of her third dive,
[tex]d_3 = -(7.8 + 2\times 2\dfrac{1}{8})\\\\d_3 = 12.05\ feet[/tex]
Therefore, the depths of her second and third dives is -9.925 feet and -12.05 feet.
Hence, this is the required solution.
