Toby wants to increase his test score average by 10% write an expression that he can use to determine his new grade will be

Let x = Toby's current test average.

Then: x +.10x would get you to an average that is is 10% greater.

Example: Lets say your current test score average is 80. 10% of 80 is 8. So 88 represents a 10% increase compared to 80.

Or, think of what 110% of 80 would be: 1.1 (80) = 88