少数の読み方はGrade5の内容です。
少数を正式に英語で読むのは大変です。
簡略な方法で済ませるのが妥当でしょう。
BBC
http://teach.files.bbci.co.uk/skillswise/ma04deci-e3-f-the-decimal-point-and-reading-decimals.pdf
When reading decimals out loud you have to read the number after the decimal point, one at a time. For example:
1.5 is ‘one point five’
12.06 is ‘twelve point zero six’
1.25 m is ‘one point two five metres’