The same price can be written at least four ways. Converting between them takes one line of arithmetic each.
Decimal odds state the total returned per unit staked, including the stake. At 2.50, a stake of 100 returns 250, of which 150 is profit. This is the standard in most of Europe and across much of Asia.
Fractional odds state profit relative to stake. 3/2 means three units of profit for every two staked. To convert to decimal, divide and add one: 3 divided by 2 is 1.5, plus 1 is 2.50.
A positive number is the profit on a stake of 100. A negative number is the stake needed to win 100.
Hong Kong odds are decimal odds without the stake. 1.50 in Hong Kong format is 2.50 in decimal. Simply add one.
Comparing prices across sites is only possible in a common format. Decimal is the easiest to compare and to turn into a probability, which is covered in implied probability and the margin. A general reference on notation is Wikipedia's article on odds.
Local guides tend to work in decimal. A clear one in Traditional Chinese is this explainer on reading sports odds and working back to implied probability and the margin (運彩賠率怎麼讀), which shows the same sums with local examples.