exam Maths Puzzle Numerical Ability

hey could you please help me out with this permutation problem:

P(n,5)=20P(n,3)

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exam Other Question

two ships leave a harbor traveling on courses that have an angle of 120 degrees between them. if they each travel 515 miles how far apart are they (to the nearest mile)? Please help...
write the equation of the parabola in standard form given the following properties.
focus: (-5/2,0)
directrix x= -4