In order to build a polynomial we need one or more terms. A term is a number, variable (denoted by a letter) or any combination of numbers and variables held together by multiplication. The following are examples of terms:

Now it might look like one of those involves division but it can be thought of as multiplication by (2/5). When we do this the exponents must be positive.
Polynomials are expressions made up of terms held together by addition and subtraction. Again, the exponents must be positive. Since polynomials are made up of the sum or difference of terms, adding or subtracting polynomials just leads to more polynomials. Here are some examples of Polynomials:

Now let’s consider what happens if we multiply polynomials. As an example we use:

What you might notice is that multiplication will lead us to multiply terms (but multiplying terms gives us more term,as) and also to add or subtract terms but that just gives more polynomials. Therefore multiplication leads to more polynomials.
Finally, we consider division. Here a simple example will do the trick: 2 is a term and x is a term. Let us divide 2 by x. We get:

which is not a polynomial because we have a negative exponent.
Thus, the answer to your question is division. Division of polynomials will not always result in a polynomial.
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is.
To change a decimal to a fraction, we simply "use as many zeros as there are decimals and lose the dot".
say in this case, 0.8 has 1 decimal, so we'll use one zero at the bottom,
Estimate this product first. 7 times 2 would be 14; 7 times 3 would be 21. So the actual product must be about halfway between 14 and 21, or 17.5.
The actual product 7*2.6 comes out to 18.2 (which is fairly close to 17.5, but not close at all to 14).