One day after school, Isabel Hughes was looking over math homework with her dad. The 12-year-old wanted to use a calculator that made fractions easier, but there were no traditional calculators to do this, nor any apps that did the trick.

So she and her dad decided to make one called Fraction Calculator. Now, the father-daughter super-team are the proud developers of best-selling calculator apps sold across several platforms.

Aidan Hughes and his daughter, both from Redmond, developed Fraction Calculator as well as Calculator Plus, apps that are essentially stock calculators on steroids. Calculator Plus has more than one million downloads and is the number one calculator app for the Kindle Fire. It’s also the second-highest rated app in all categories out of 66,280 apps on Amazon’s Android Appstore.

The Fraction Calculator features a three-keypad layout to enter fractions and a large display that shows fractions the way you write them.

The cool thing about Calculator Plus is that it remembers everything you calculate, an idea that came from Isabel.

“Belle was fully involved in planning the app, tweaking the look and feel, and testing the versions we made until it was perfect,” Hughes said. “She also put her Spanish immersion schooling to good use by translating it into Spanish.”

Belle does seem like a technology whiz. She once visited Bing as a 10-year-old and suggested an improvement to their image search, which was then implemented worldwide.

But it’s other hobbies that she’s really passionate about.

“She likes technology, but her real loves are singing and volleyball,” Aidan Hughes says. “She likes coming up with ideas though.”

Those ideas have helped the apps built under Digitalchemy, Hughes’ 2-year-old startup. The 41-year-old Dublin native previously worked at Microsoft where he held a number of roles at the company, including Development Manager, Product Unit Manager, and ultimately the Lead Program Manager for the Windows 8 App Store during planning.

But after talking to his app developer friends, Hughes knew that he wanted in on the fun so he traded in his 401(k) and started Digitalchemy with Micah Koffron. The company, which is Hughes’ second startup, originally started with the idea of making perfect everyday apps.

“The calculators were a good fit for that passion,” Hughes said.

Does he miss Microsoft?

“I love the startup world — it’s fast paced and endlessly fascinating,” he says. “But I do miss vacations, sleep, and the peace of mind of a regular paycheck.”

Calculator Plus is available on Android, iOS and Windows, while Fraction is on Android and iOS as well.