70% of 135 is 94.5, meaning you can miss out no more than 40 questions to pass the exam.
To calculate percentages easily, use this free online percentage calculator.
Several aids that will help you solve percent word problems (from CNM.edu):
1. Make sure you understand the question that is asked
2. Sort out the information to make a basic percent problem, such as “30% of what is 17?”
3. Sometimes, you will have to subtract or add some of the numbers.
4. The base will always be the original number, price, or total.
For free printable percentage worksheets, go to HomeschoolMath.net.