DIET Archives | Math for Grownups

you’ve read a women’s magazine or watched one of Oprah’s weight loss shows, you know a thing or two about how to shed those pounds. Move more, eat less, right?

You probably also know how easily we can be fooled by diet companies and nutrition labels. One of those bags of chips you buy at the gas station between errands? The package may claim 250 calories per serving, but the bag may actually contain 2.5 servings.

It’s that tiny little word — per — that screws us up. It’s so little, you might not even notice it. But it can make a big difference between reaching your weight goal and wearing a muumuu on the beach this summer.

If you think back to your elementary or middle school math classes, you may remember your teacher explaining that per means each. And if you think even harder, you might remember the operation (addition, subtraction, multiplication or division) that is indicated by the word per.

Yep, it’s good old division. Think of it this way:

Charlie has six Star Wars figures, and he’s playing with two friends.
“But I want all of them,” he screams. To which you calmly reply, “I know, but that’s not fair. How can we be fair?”
“They can have none, and I can have all of them,” says Charlie, stubbornly.
This is why we teach kids division, you think.

In that situation, you know without a doubt that dividing the Star Wars figures evenly between Charlie and his two friends is not only fair but easy: Because there are six toys and three friends, each friend gets two figures. In other words, there are two figures per child.

You did that in your head, but the math works out.

6 toys ÷ 3 friends = 2 toys per friend

Now, look more carefully at the above statement. Toys per friend translates to 6 ÷ 3 or 2, right? And that means that per means to divide.

Got it? Good. Now you can apply this any time you see the word per. In fact, this is precisely what I did on Wednesday, when I was figuring out how long it would take me to lose 25 pounds.

Whatever you expect to lose in a week, the math is simple:
total weight lost goal ÷ loss per week = number of weeks
25 pounds ÷ 1 pounds per week = 25 weeks
So if you think you can lose 2 pounds per week, it’ll take you 12.5 weeks to lose 25 pounds:
25 pounds ÷ 2 pounds per week = 12.5 weeks

Remember, I also wanted to convert the number of weeks to months — because that’s how my brain works:

I already figured out that I can probably reach my goal in 25 weeks. To find out how many months that is, I can just divide by 4 (the number of full weeks in a month):
25 weeks ÷ 4 weeks per month = 6.25 months

This works for a variety of calculations you may make when embarking on a plan to reach your fitness and weight loss goals. If your trainer says you should exercise for 5 hours per week, you can divide this in a variety of ways:

5 hours ÷ 5 days = 1 hour per day

5 hours ÷ 4 days = 1.25 hours per day

5 hours ÷ 6 days = 0.83 hours per day (or 50 minutes per day)

And so on.

If you practice this skill, you’ll find yourself doing it all over the place — translating miles per hour to your estimated time of arrival, figuring out how many cheddar cheese goldfish are in a half-serving, calculating the exact number of stickers each of your triplets get from the package, and so on.

So get on with your bad self. Use per to your advantage and don’t let servings trick you into eating more than you wanted to.

When do you use division (and per) to help with your fitness and weight loss goals? Share your thoughts in the comments section.

I suspect I’m not alone in one of my New Years resolutions: to eat better, exercise more and lose weight. (Ack! Did I just write that out loud?) Like other women in their mid-forties, I have found my metabolism screeching to a halt and my weight creeping up and up. So last night, I launched my most recent — and hopefully last — attempt at getting into better habits.

But I’m not fooling myself. This is a long process with a lot of little steps, some forwards and a few backwards. My issue is staying motivated. I do well for a while, and then I slip up — and eventually give up. So, I’ve got a good plan that should allow me to make incremental changes and leave lots of room for mistakes. And to accomplish this, I’ve got both measurable and soft goals.

Sure, I want to eat better (I can count each serving of veggies I eat or glass of water I drink.) And I want to exercise more. (I can count my hours at the gym or steps I take from my car to the grocery store.) But for me, those are big changes that will include a lot of frustrating missteps. In order to stay focused, the real measurement will be my weight.

My goal is to lose 25 pounds. And I’ll track this by weighing myself once a week.

So how long will it take me to lose the weight? This is where the math comes in. Here’s what I know:

I want to lose a total of 25 pounds.
I will probably lose between 0.5 and 2 pounds each week.

Does this mean I’ll be sitting on a beach in a string bikini in August? (That’s a joke. I’ve never worn a bikini in my life.) Let’s look at the math.

A half pound and two pounds is a pretty wide spread, so based on past experience and my inclination to be more conservative, I’m going to estimate that can lose about a pound each week. So I can reasonably expect to lose all of the weight in 25 weeks.

Whatever you expect to lose in a week, the math is simple:

total weight lost goal ÷ loss per week = number of weeks

25 pounds ÷ 1 pounds per week = 25 weeks

So if you think you can lose 2 pounds per week, it’ll take you 12.5 weeks to lose 25 pounds:

25 pounds ÷ 2 pounds per week = 12.5 weeks

But there’s one more step I need to take. I don’t think in terms of weeks. My brain focuses on months. How many months will it take me to lose the weight?

Again, I’m going to estimate. While there are approximately four weeks in each month, that’s not an exact figure (except in February during a non-leap year). But since I’m not measuring out medication or figuring out how much to send into the mortgage company or solving problems for my eighth grade math teacher, I don’t have to be exact. So I’m going to go with four weeks in a month.

I already figured out that I can probably reach my goal in 25 weeks. To find out how many months that is, I can just divide by 4 (the number of full weeks in a month):

25 weeks ÷ 4 weeks per month = 6.25 months

Ta da! I can reasonably expect to lose this weight in six months. That means if all goes well, I should be at my goal by June.

Like me, are you hoping to lose weight in 2012? Do the math to see when you’re likely to reach your goal. And if you want to share, feel free in the comments section. (It’s scary, but you can do it!)Save

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