The correct answer is y < 18. Let's pretend a student forgot to flip the symbol and they mistakenly believe the solution set is y > 18. They check 21 since 21 is greater than 18, and they think that y has to be greater than 18. When they do their check, what will the final line of the check say? Is this a true statement?

It is wrong

Step-by-step explanation:

y < 18

This is read as y is less than 18. If the students forgot to flip the symbol and mistakenly believe that y > 18.

y > 18

This is read as y is greater than 18.

There is a difference between the numbers greater or less than 18 .

y must have numbers less than 18 and 21 is greater than 18.

Therefore it is wrong.

But to make it true we can multiply minus with the inequality y > 18

-y > -18

This reverses the inequality sign and it becomes

y< 18

The solution which is required.

0.2

You have to first write out the numbers. Once you write them out, you are going to put 4x10^4 over 2x10^5 (so divide.) You are first going to divide the base numbers 4/2= 2. Then you are going to divide the powers of 10. 10^4/10^5 ( you just subtract the exponents), 10^-1. Your final equation will be 2x 10^-1. Finally put it in standard notation, 0.2.