An estimate helps you place the decimal point when multiplying because if you find out how many decimals there are and once you are done doing you estimated multiplication you put two decimal points after that.
Hope I helped some what and didn't make you confused.
To find the value of 1 out of all pieces divided, add the ratios.
8+1= 9
Now divide 72 by the total number.
72/9 = 8 (the value of one 1 unit)
Now to find the value of 8 units= 8*8 = 64
Value of 1 unit= 8
Yes you need to! And you need to be careful not to forgot that when doing your calculations!!
