[racket] Help with filter-map

From: Joe Gilray (jgilray at gmail.com)
Date: Mon May 28 01:37:54 EDT 2012

I created some Racket solutions to ProjectEuler #71.  Below is one that
uses filter and map:

(define (euler71c)
  (numerator (apply max (filter (λ (n) (> (/ 3 7) n)) (map (λ (n) (/ (floor
(/ (* n 3) 7)) n)) (stream->list (in-range 2 1000000)))))))

1) I thought I might speed it up by using filter-map, but I cannot
understand how to do it.  I read the 1 line I could find in the reference
and it just doesn't help me

2) The code above takes about 4x the time of a simple for loop
implementation.  What can I do to speed it up?

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