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(define factorial
  (lambda (n)
    (if (= n 0) 1
        (* n (factorial (- n 1))))))


(define (combination n b)
        ( / (factorial n) ( * (factorial (- n b)) (factorial b)) ))

(define (my_prob n p b)
        ( * (combination n b) ( * (expt p b)  (expt (- 1 p) (- p b)) )))

(define (atleast_b n b p)
        (if (> b n)
                0 (+ (my_prob n b p) (atleast_b n (+ b 1) p)  )))

(atleast_b 10 3 0.3)