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K. 532. Greg charges the battery of his cell phone every night, so he can start every new day with a 100% charged battery. If he only uses the phone for talking, the battery lasts 30% longer than when he plays games with it, and it lasts 60% longer than when he is surfing the net. Today, he has talked for 20 minutes on the phone, played for 50 minutes, and spent 80 minutes on the net. The battery is now flat. How long may Greg use the internet with his phone if it is fully charged, and he does not use it for anything else?

(6 points)

This problem is for grade 9 students only.

Deadline expired on 10 February 2017.

Google Translation (Sorry, the solution is published in Hungarian only.)

Megoldás. Gergő a mai napot tekintve $\displaystyle 20 + 1,3\cdot50 + 1,6\cdot80 = 213$ percig tudott volna beszélni. Ezt osztva 1,6-del kapjuk meg azt, hogy egy teljesen feltöltött telefonnal mennyi ideig tud internetezni: $\displaystyle 213:1,6=133,125$ percig.

Statistics on problem K. 532.
 81 students sent a solution. 6 points: 67 students. 5 points: 8 students. 4 points: 5 students. 3 points: 1 student.

• Problems in Mathematics of KöMaL, January 2017

•  Támogatóink: Morgan Stanley