Four pence can buy seven bitter fruits, and eleven pence can buy nine sweet fruits, with an average of 4/7 pence for each bitter fruit and sweet fruit 1 1/9 pence.

If there are x sweet fruits, sweet fruits need 1 1/9*X, and bitter fruits need 999-1/9 * x.

( 1000-X)* 4/7 = 999- 1 1/9 * X

X=637 and 1000-X=363 can be obtained by solving.

So the sweet fruit and bitter fruit are 637 and 363 respectively.