1/10 is the same as 0.1. Therefore it is the same as asking 0.1*5.4 =0.54
To work it out you can think if I removed the decimal points out of both numbers it would be just 1*54 making it equal 54. 54 is the same as 54.0, and if you look at the question and count the decimal places in both numbers it is 2. Now move the decimal place in the 54.0 2 places and you get 0.54