Kathleen must get 300 signatures to make sure she will have enough valid signatures for the crosswalk
Solution:
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
[tex]x - 20 \% \times x = 240\\\\x - \frac{20}{100} \times x = 240\\\\x - 0.2x = 240\\\\0.8x = 240\\\\x = 300[/tex]
Therefore, she must get 300 signatures so that she will have enough valid signatures for the crosswalk
