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Expert: - 6/9/2009


Question
I am trying to figure how to solve decimals with nothing to borrow from.  Ex... 0.0025 - 0.075, 0.9- 76.78, 6.241 - 37.7293.  I have seen the answers and used a calculator but, I don't understand how 0.0025- 0.075= 0.075. I saw one website that renamed the first zero with a 7 on several problems.  Why would you do that? Please help. How do you subtract decimals with nothing to borrow from?


Answer

Subtraction
The best way to subtract a large number from a smaller number is to reverse them.  When finished, note that the answer should be changed to negative.
The first one, 0.0025-0.075, would turn into 0.075 - 0.0025.
Note that there should be the same number of terms after the decimal.

If there are not, add a 0 to the shorter one until there are.

Looking at the problem, 0.075 only has three digits past the decimal, whereas 0.0025 has four digits past the decimal.
That means we need to add a 0 to 0.075 to get 0.0750.

We can now do 0.0750 - 0.0025.
To do this, look at the last digit.  

We have 0 in the first number and 5 in the second.
This means that we have to borrow 1 from the 5 in 0.075.
This makes 0.075 into 0.074 and we now instead of just a 0,
we have 10.  Now 10 - 5 is 5, so that goes down below the two.

What we are left with in the problem is 0.074 - 0.002.
Looking at the last digits, 4 and 2, 4-2 = 2, so 0.074 becomes 0.072.
Now remember the five up above?  It should have been written down already. so the answer is 0.0725.

I'll put the rest of these in a attached file
, 0.9- 76.78, 6.241 - 37.7293

Scott A Wilson

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