An image of McDonald's menu this week went viral because people couldn't believe the prices depicted. Twitter user Sam Learner says he snapped the photo at a McDonald's located at a Connecticut rest stop. In the photo, a Big Mac combo meal – with fries and a soft drink – is $17.59.

Other combo meals, like a Quarter Pounder with bacon and cheese, are priced at $18.99 in the photo. Menu prices for many restaurants are often higher on delivery apps than in-store. On GrubHub, a Big Mac combo meal from the Darien location will set you back $21.59. 

The high prices stand out, considering the fast food chain is known for low-priced food and even boasts a $1 menu at many locations.

After discovering the expensive McDonald's off of I-95 in Darien, Learner said he looked into the company's prices a bit more. "Ok, I did a little digging and I think I might have stumbled into the country's most expensive McDonald's," he tweeted. 

Using data from Pantry and Larder, a food research site, Learner found a McDonald's in Lee, Massachusetts, lists a Big Mac for $8.09. Still, the Darien location lists a more expensive Big Mac for $8.29.

According to budgeting site SavingSpot, the U.S. has the 19th most expensive Big Mac in the world, with an average cost of $5.35. Sweden has the most expensive Big Mac at $7.75, according to the site. 

Some social media users were outraged by Learner's post. Some compared the Darien prices to McDonald's in their area. "Checking my local McD's in the bay area, a #1 Big Mac meal is $10.48, so the rest stop has a ~70% markup," one person replied.

Others urged Learner not to spend that much on a Big Mac. 

Many suggested that the prices could be inflated at rest stop locations. Others blamed it on Connecticut – particularly Darien – being an expensive place to live.

At a freestanding McDonald's location in Stamford, just about 10 miles from Darien, a Big Mac meal with fries and a soft drink is $11.79 on GrubHub – above the national average. 

At the Darien rest stop location, the same meal is a whopping $21.59 on GrubHub. 

The Darien location shows above-average prices for many items, according to Learner's photo and the GrubHub page for that location. On the delivery app, a Sausage Egg McMuffin Meal, which comes with a hash brown and coffee, costs $17.39 at the Darien location. The same meal at a McDonald's in the Upper East Side of New York City costs $8.29 on GrugHub. 

The median household income in the Upper East Side, which is considered one of the most expensive neighborhoods in the city, is $138,490. That's about 92% higher than median household income citywide – $72,150.

The median household income in Darien, one of the wealthiest towns in Connecticut, is $250,001. That's 57% higher than the median household income in the Upper East Side — but McDonald's prices there are about 70% higher. I

Minimum wage in both Connecticut and New York City is $15 an hour. 

So, what affects the price differences between McDonald's locations? The owners. About 90% of McDonald's locations are independently owned, and the franchisees have the ability to set their own prices, McDonald's says. That's why the company doesn't list prices on its corporate site – prices vary depending on where you are. 

The price at the Darien location on the Connecticut Turnpike takes into account costs associated with operating a McDonald's on that highway. 

The two states with the highest average Big Mac price are Hawaii for $5.31 and New York for $5.23, according to SavingSpot. Mississippi has the cheapest at $3.91. 

CBS News has reached out to McDonald's corporate as well as the Darien location and is awaiting response. 

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Caitlin O'Kane is a digital content producer covering trending stories for CBS News and its good news brand, The Uplift.