If Olive charges her phone for 3/5 of the time she charged the phone last night, the phone would be charged for 3/5*10=<<3/5*10=6>>6 hours.
Assuming each hour of charge lasts the phone 2 hours of use, the phone will last for 6*2=<<6*2=12>>12 hours before it goes off when Olive uses it on a six hours charge.
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