Phoebe eats 1 serving and gives her dog 1 serving of peanut butter for a bedtime snack. Each jar of peanut butter has 15 servings.  How many jars will she need to make sure she and her dog have enough to last for 30 days?
She and her dog both have a serving before bed so they eat 1+1 = <<1+1=2>>2 servings a day
She wants to have enough for 30 days and they eat 2 servings a day so they need 30*2 = <<30*2=60>>60 servings
Each jar has 15 servings and she needs 60 servings so she will need 60/15 = <<60/15=4>>4 jars of peanut butter
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