Take an example using money. If you are used to American money you will know that 10 cents is a tenth of a dollar, so 30 cents is 3 tenths, written 3/10, of a dollar. It is also written $0.30 and 0.30 or simply 0.3 represents 3 tenths, too. 3 dimes make 3/10 of a dollar. So you can think of a dime as one tenth (1/10).
The English pound (£) is similar to the US dollar, and a cent is called a penny (as in USA). 10 pence (10p) is a tenth of a pound because 10 times 10 pence is 100 pence, which is a pound. So 30p is 3/10 of a pound.