"I found it a bit tedious, all those additions and multiplications, so I reckoned, 'We already have intelligent software, why not make it deal with maths?'" Sabol said.
The result was PhotoMath, a free app that scans and solves equations, providing a step-by-step explanation. It has been downloaded more than 11 million times since its introduction in October, and it was just updated on Thursday to take it to high school level. An Android version was released this week.
The app is based on the same technology as an earlier app called PhotoPay that was introduced in 2012 by Sabol's company, which is also called Photo Pay. That app facilitates mobile banking, by scanning household bills and paying them instantly.
"Basically, what we do is teach mobile phones to read things from the real world," Sabol told Reuters in his sparsely decorated office in Zagreb, where a dozen young software engineers jot down ideas and algorithms.
He said the PhotoMath averages about 1.5 million users every month and he had received scores of emails from grateful students, parents and even teachers.
"Will I allow my pupils to use the app? Absolutely," a British maths teacher wrote on www.amathsteacherwrites.co.uk, after a pupil proudly presented the app in class.
"As a means for them to check their work it's unrivalled ... They are far more likely to 'listen' to an electronic device, rather than teacher, telling them that they are right or wrong," the teacher wrote.
Sabol says he has never regretted making the app available for free.
"Now, of course, we are looking for ways to be commercial," he said. "Without that, we cannot continue developing the app.
© Thomson Reuters 2015
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