20/30 as a decimal rounded to the nearest tenth

0.7

Step-by-step explanation:

30 cannot be multiplied to give a power of 10, so to find the decimal you have to divide: 2/3 = 2/3 + 2 : 3

2 divided by 3 is 0.6666666 ... It is a recurring decimal.

However it is not practical to use recurring decimals in calculations, so the decimal is usually rounded off to 2 or 3 decimal places depending on the accuracy required for the answer.