I am pretty sure it is talking about interest and $640 is what you start with, with a 3% interest for 2 years
A
rational number is any number that can be written as the
ratio between two other numbers i.e. in the form

Part A:
An easy choice that makes sense is 7.8, right in the middle. To prove that it's rational we need to write it as a ratio. In this case we have

Part B:
We need a number that can't be written as a ratio (because it neither terminates nor repeats). Some common ones are

,

,

and

so it makes sense to try and use those to build our number. In this case

works nicely.
Answer:
IJ
Step-by-step explanation:
You can't change the sum by changing the grouping. Any way you cut it, you will always get 226, as you only have addition operations, and the commutative property [a+(b+c)=(a+b)+c] means that the sum will always be the same.