0.4 is already written as a decimal because out of 4 out of 10 which is 40 percent. The 10 is from where the 4 is for example the number 4 on your question is the tenth place so tenth place equals 10 so... =4/10
Honestly? Just review your notes and try to work out the problems yourself before taking a look at the answer. You can also google specific topics that the test will cover and try the practice problems.
