Kathleen must get 300 signatures to make sure she will have enough valid signatures for the crosswalk
<em><u>Solution:</u></em>
Given that Kathleen needs 240 valid signatures on a petition to get a crosswalk installed on her street
She knows that about 20% of the signatures will not be valid for a variety of reasons
Let "x" be the number of signatures
invalid signature = 20 % of x
valid signatures = 240
Then, according to question,
total number of signatures - invalid signatures = 240
x - 20 % of x = 240
Therefore, she must get 300 signatures so that she will have enough valid signatures for the crosswalk