Update README.md

Author: cs-MohamedAyman

level-3/hackerearth-phase-3-mathematics-strings/README.md

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 <img align="right" width="80" height="80" src="https://github.com/cs-MohamedAyman/Problem-Solving-Training/blob/master/online-judges-logos/hackerearth.jpg">
 
-## [HackerEarth](https://hackerearth.com/) OJ - Mathematical & Strings Algorithms `150 problems` `80 hrs`
+## [HackerEarth](https://hackerearth.com/) OJ - Mathematical & Strings Algorithms `230 problems` `120 hrs`
 
 ### Table of Content