I do love a good divisibility rule.

Recently, I asked the BuzzFeed Community fortheir best math trick.

The answers are remarkably useful, so without further ado, here they are!

Animated characters arguing about math changes, text reads "WHY WOULD THEY CHANGE MATH? MATH IS MATH!"

1.“Sales!

If something is 70% off, you are paying 30%.

5.Divisibility rules are wildly useful.

Handwritten math calculations showing a discount problem, with a pen resting on the paper

“When I add, I break it down and do easy first, then hard.

“The nines multiplication hand trick!”

You could even take it a next step by saying 39 is 1 away from 40.

Handwritten math notes on finding the area of an equilateral octagon, with a pen resting on the paper

Handwritten math equations with mistakes and a pen to the right side

Handwritten note solving a math problem to double a recipe that requires 3/8 cup of flour, resulting in 6/8 cup or simplified to 3/4 cup

Handwritten math divisibility rules with a pen resting on the paper

Handwritten math showing that 18% of 50 equals 50% of 18, both equal 9, with a pen resting on paper

Handwritten math division problems on lined paper with a pen

Handwritten math calculations on lined paper with a pen resting on it

Handwritten note explaining a multiplication trick for 9 with sketches of hands counting. Summarizes 9x4 using fingers, result is 36

Handwritten math problem on paper with a calculation mistake corrected for summing 250 and 18, then subtracting 1