A rather unique and interesting feature of Clojure (and Lisp derived languages) is the first class support for rational numbers.

1/3
-5/3
(type 1/3)
;= clojure.lang.Ratio

Rational arithmetic is also supported:

(- 3/5 (+ 1/3 4/5))
;= -8/15

And it does an automatic simplification when possible

10/25
;= 2/5

Be careful when mixing rationals with floating point numbers as the result will default to Double (and lose precision).

(+ 1/3 0.3)
;= 0.6333333333333333
(type (+ 1/3 0.3))
;= java.lang.Double

If you wish to preserve rationals when mixed with floating points in computations you can use the rationalize function.

(rationalize 0.3)
;= 3/10
(+ 1/3 (rationalize 0.3))
;= 19/30
(type (+ 1/3 (rationalize 0.3)))
;= clojure.lang.Ratio

The caveats of using rational is that the performance drops drastically in favour of precision.