vous savez que
a/b x c/d = axc / bxd
donc
3/7 x 8/3 = (3x8) / (7x3) = 8/7
et
2/15 x 15/11 = (2x15) / (15x11) = 22/11
et
14/23 x 1/7 = (14x1) / (23x7) = (7x2x1) / (23x7) = 2/23
et
2/11 x 3/4 = (2x3) / (11x2x2) = 3/22
et
7/8 x 1/21 = (7x1) / (8x3x7) = ... / ...
et
2/3 x 3/4 x 4/5 = (2x3x4) / (3x4x5) = ... / ...