here is a neat trick:
write down the two fractions without any "sign" between them
19/6 4/27
first write down the cross-product from topleft to bottomright
459
leave a space then write down the crossproduct from topright to bottomleft
459 36
Place the correct relationship sign, = > or <, between them AND the original fraction.
since 459 > 36
19/6 > 4/27 , so the proportion is false.
another example
17/24 4/5
65 96
since 65< 96
17/24 < 4/8
another
9/12 36/48
432 432
since 432 = 432
9/12 = 36/48