Remark
The upper answer is correct. Any time you are dealing with addition or subtraction and one of the numbers is irreducible and remains irrational no matter what you do, then the entire addition or subtraction of terms remains irrational.
For the second one that you did not answer, it works the same way as the comment says.
3√2 * 8√18 give two numbers that can be multiplied under the square root sign.
3*8 = 24
√(2*18) = √(36) = 6
The answer is 24*6 = 144
This procedure is the only way I know that you can get a rational result from two irrational factors. In fact it is really quite useful to know. You will use this when you learn how to rationalize the denominator. This exact method is used to do that.
2.2 is the answer because when you divide its a decimal
3%
the percentage of 7 out of 39 is 2.73. If you round it is 3%
I hope this helps!
