Question

How do you evaluate `6.38- 2.4`?

Answer 1

`3.98`

Explanation:

Notice that the 4 from 2.4 is more than the 3 from 6.38
So 3 - 4 part needs a bit of thinking about. Lets change the 6.38 so that it is easier to subtract the 4 from the 3.

Note that 1 is the same value as `10/10`

`color(blue)("Changing the way that 6.38 looks to make the maths easier")`

By way of explanation lets write 6.38 as `6+3/10+8/100`

But 6 is the same as `5+10/10` so now we write

`5+10/10+3/10+8/100`

This is the same as
`5+13/10+8/100`

Writing this in decimal form we have:

`6.38" "->" "cancel(6)^5. cancel(3)^(13)8`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`color(blue)("Putting it all together and doing the subtraction")`

`cancel(6)^5. cancel(3)^(13)8`
`ul(2 color(white)(..).4color(white)(....)0 larr" subtract"`
`3color(white)(..).9color(white)(....)8`

Answer 2

`3.98`

Explanation:

`6.38-2.4`

`:.=6 38/100-2 4/10`

`:.=638/100-24/10`

`:.=(638-240)/100`

`:.=398/100`

`:.=3.98`