10. The heater of an electric kettle has two sections. When you turn on one of them in a pot to boil water after a time t1 = 15 min, when the other - after a time t2 = 30 min. How long tzakipit water in the kettle, if you include the two sections: a) series; b) in parallel?

Detailed solution. Decorated in Microsoft Word 2003. (Target decided to use formula editor)