Happen Bank Software Engineering Returnship interview questions

I had an online interview and was provided link to use an online coding tool I believe called coding pad. The tech lead asking questions was very pleasant but he basically asked me a question that seemed to be testing my mathematical knowledge instead of my coding knowledge. He tried to help me along, but I was totally unprepared with the math knowledge required to solve the problem and as such could not finish coding in the required time. If I were in his shoes, I would change strategy with respect to candidate rather than be hung up on the Math problem.