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It’s the last post of June, but we have a lot more summer to go. That means a lot more opportunities to enjoy the outdoors — and expose ourselves to damaging UV rays. Not only is a burn uncomfortable (or downright painful), but it comes with a whole host of other problems, from wrinkles to cancer. Take a look at these facts from the Skin Cancer Foundation:

  • More than 3.5 million skin cancers in over two million people are diagnosed annually. That’s more than the combined incidence of cancers of the breast, prostate, lung and colon.
  • One in five Americans will develop skin cancer in the course of a lifetime.
  • Over the past 31 years, more people have had skin cancer than all other cancers combined.
  • Between 40 and 50 percent of Americans who live to age 65 will have skin cancer at least once.
  • One person dies of melanoma every 62 minutes.
  • One or more blistering sunburns in childhood or adolescence more than double a person’s chances of developing melanoma later in life.
  • A person’s risk for melanoma doubles if he or she has had more than five sunburns at any age.

So that’s a lot of numbers and statistics. (Believe me, I only shared a fraction of what I found.) But there are other really important numbers to consider: SPF or sun protection factor.

Basically, SPF is the estimate of time that you can be in the sun without burning. This is really easy math. Let’s assume that without sunscreen, you would burn after 15 minutes. If you used a sunscreen with SPF 15, you’d be able to stay in the sun 15 times as long without burning:

15 minutes • 15 = 225 minutes

225 minutes ÷ 60 = 3.75 hours

If you used a sunscreen with SPF 30, you be able to stay out twice as long:

15 minutes • 30 = 450 minutes

450 minutes ÷ 60 = 7.5 hours

But can you add SPF values? In other words, if you put on SPF 15 and then SPF 30, would you have SPF 45? Mathematically speaking, yes. But in actuality, nope. You’re only as good as the highest SPF you applied.

It’s also important to note that SPF ratings are averages. So while these calculations can help protect you from a nasty burn, you can’t count on them for down-to-the-minute protection. (There’s that imprecision-of-math thing again.)

There are also many, many other variables to consider — including time of day (sun exposure is harshest between 10:00 a.m. and 2:00 p.m.), location (water and sand reflect light, intensifying the rays) and activity levels (sweat and water can cause sunscreen to wear off).

The bottom line? You can do all of the calculating you want, but the only sure-fire way to prevent a sunburn — and the health risks associated with it — is to avoid the sun. Protective clothing can help, along with staying out of the sun when it’s at its strongest. And look for new labeling on sunscreen products. Last summer, the Food and Drug Administration (FDA) introduced new rules for these products, which will start showing up next summer.

This is perhaps the most basic math of all, so there’s no need to make it complicated. For once, you don’t need to multiply or do figures in your head. Just follow these simple rules:

1. Wear the highest reasonable SPF levels. (The FDA says SPF 50 is the best you can do.)

2. Everyone needs sunscreen. All skin types can burn or at least suffer from skin damage. So even if you have dark skin, apply sunscreen.

3. Cover up as much as possible, with broad hats, swim shirts and umbrellas.

4. Avoid the sun at peak times, especially if you plan to be on the water or beach.

5. Reapply sunscreen at least every two hours, more often if you’re sweating or getting in and out of the water.

Simple, eh?

How do you manage the sun and outdoor activities in the summer? If you have cool tips to share, post them in the comments section!

On Monday, we’ll take off on a month of travel math. Got questions? Let me know, and I’ll track down the answers.

I grew up a few miles from the Appalachian Trail in Southwest Virginia and my grandparents lived in the Shenandoah Valley, near Big Meadows a popular stop-off for trail hikers. While I’ve never had any inclination to take the entire trail from Georgia to Maine, I have done a few tiny sections — an hour or two hike each.

It’s way too late in the year to start a thru-hike (doing the entire trail), but a section hike would be perfect for a lazy summer day. These are generally less than 5 miles, though you could string together two or more for a weekend adventure. And if you’re nowhere near the Appalachian Trail, just choose another trail to explore.

But how much time should you allot for your hike? This is an important consideration, since it will determine the time you set out (there are no lights on the trail, so once the sun sets, it’s black as pitch) and what you’ll need to bring (food and water are essentials if you’re planning to be gone more than an hour or so).

Experienced hikers can probably gauge how long it will take to hike a given number of miles. But if you’re like me, you don’t have a clue. That’s where pace counting comes in. The length of your stride will tell you how many steps it will take you to go a certain distance. From that, you can get a good estimate of how long it will take you to complete the hike.

To measure the length of your stride, you’ll need two pens, a tape measure and a long hallway or sidewalk. Place one pen at the end of the hallway or sidewalk and stand with your feet together and hells against the pen. Now, walk 10 steps, taking normal strides. After the tenth step, bring your feet together again, and place the second pen behind your heels. Measure the distance between the pens, using the tape measure. Then divide by 10 to find your stride length. Ta-da!

Another method is to estimate your stride based on your height. There’s a simple formula for this, but you’ll first need to have your height converted to centimeters. If you’re a man, multiply your height (in cm) by 0.415; women will multiply by 0.413.

Once you have your stride length, you can use this to estimate the number of strides you’ll take when hiking a particular distance. Let’s say your stride is 28 inches long, and you’re hiking the Chestnut Knobsection in Virginia, which is 2.6 miles round trip. How many steps will you take in that hike?

Ultimately, you’re going to divide the total hike by the length of each stride. But that means you need to have these measurements in the same unit. In other words, you need to convert 2.6 miles to inches. There are 63,360 inches in a mile, so the entire hike is 2.6 • 63,360 or 164,736 inches. Now divide, to find the total number of strides:

164,736 ÷ 28 = 5,883

So on this hike, you’ll be taking a total of 5,883 strides. Still, you don’t know how long the hike will take you, right?

For that step, you need to know how long it takes you to walk a certain number of strides. Let’s go back to the where you found your stride length. If you timed how long it takes you to walk 10 paces, you can easily find the time, right? All you need to do then is use a stopwatch while you take 10 paces. Let’s say that value is 6 seconds. A little bit of math will get you closer to your answer.

First, divide the total paces by 10. Why? Because your time is based on 10 paces, not one.

5,883 ÷ 10 = 588.3

Now multiply this answer by 6 or the number of seconds it takes to walk 10 strides.

588.3 • 6 = 3,529.8

So, it will take you 3,529.8 seconds to hike this section of the trail. It’s probably easier to understand, if you convert this to minutes or hours.

3,529.8 ÷ 60 = 58.83 minutes or just under an hour

Of course this estimate assumes a lot of things: that the terrain is easy to maneuver and that you’re not going to stop to look at the view of Burkes Garden. In other words, you can bet that you’ll be on the trail for longer than an hour, especially if you’re there to metaphorically or literally smell the flowers.

Still, you can use these calculations to estimate the time it will take you to complete any number of hikes. Once you know your stride length and the time it takes for you to walk 10 paces, the math is pretty simple.

What kind of hiking do you love to do? How have you used math to help you plan a hike or other outdoor activity? Share your stories in the comments section.