A new study has shown that differences in math performance between boys and girls are so small as to be statistically insignificant.* Yet, how many women do you know who claim to be completely hopeless at math? How many men? Hmm.

I think it’s more socially acceptable for women to be bad at math than for men to be, so some women just give up sooner. Imagine if there were some stereotype that women were bad at reading — that would be no excuse to just stop whenever a document, article, or ballot got complicated. The study says much the same thing: women exposed to negative stereotypes about women and math end up performing worse.

On a positive note, numbers can be fun! They help you measure how much better you are at things than other people are! Here are five steps to better living through math.

**Consecutive Discounts**

My mom worked in retail for many years, and got pretty good with percentages. The people working the registers at other stores? Sometimes, not so good. If you have a coupon for $10 off and another one for 15% off, which one do you want the cashier to ring up first? You want the percent off first, and then $10 off. If the $10 is deducted first, then you’re getting 15% off a smaller amount.

Stores are on to this, so they have rules that the coupons are supposed to be rung up in the way most advantageous to the store. The cashiers, however, sometimes don’t follow procedure. My mom is a nice person, so rather than taking the extra discount, she would gently correct the cashier, pointing out that if the cashier gave my mom extra money off, the cashier might get in trouble. Most of the cashiers didn’t actually believe that the order in which you rang up the discounts made any difference.

(Incidentally, if both discounts are percents, it doesn’t make a difference, but if one is a percent off and one is dollars off, you want the percent first! Remember PEMDAS? Yep, it’s that).

**Be Smooth at Restaurants**

People sometimes make such a big deal about figuring out a tip. It’s not hard with a few simple mental math tricks. The idea is to automate the process so you can do it when drunk.

To figure 20%, take 10% and then double it. For instance, on a $65 bill, move the decimal in one place to take 10% — that’s $6.50. Then double it — that’s $13. Add that back to $65 to get that you should pay $78.

If you’re in NYC, the restaurant tax is 8.25%, so you can simply double the amount of the tax and then round up.

If you have to figure out just how much you, personally, should pay, it’s the total of your items, plus tax and tip. (If you’re working with the whole bill, they’ve already added tax, but if you’re working with just your items, you’ll have to add the tax yourself). Adding 8.25% to a number and then adding 20% to that number is actually adding 29.9% (you can’t just add 8.25 and 20, because once the tax has been added to the bill, you’re figuring the tip on the after-tax amount — so you want to multiply the bill by 1.0825 and then 1.2, or 1.299, which is the same as adding on 29.9 percent). In a nutshell: 30% is just fine. To take 30% really fast, just move the decimal in once, and then triple.

For instance, if you had two $10 cocktails and an $18 entree, you spent $38. Move the decimal in once to get 3.8, then triple. Since 3.8 is almost 4, you need to add a little less than $12 to your total. Or, just multiply the total of your items by 1.3 on your phone. To remember 1.3, use the mnemonic: “When I was 13, I wasn’t allowed to drink cocktails in bars at all. Although in that movie *Thirteen*, Evan Rachel Wood totally drank some cocktails.”