When a child learns to relate math to everyday questions, he will be great at it from the simplest addition all the way to trigonometry. To convert percentages, decimals and fractions is thus one essential skill.
There are other sources for worksheets also. You can find many public schools and private schools which will provide free worksheets for you if you buy textbooks from the school.
In other words, they never memorized their multiplication tables! Many times I have seen a student do poorly due to a weakness in basic math facts they should have learned in third grade.
They're also available for nearly all grade levels. There are printable middle school, high school, elementary school, and even pre-school worksheets.