<human>:  Wendy's truck has a gas tank that can hold 20 gallons. She also has a car with a gas tank that holds 12 gallons. The truck's tank is half full. The car's tank is 1/3 full. If she fills them both up completely, how many gallons does she add?
<bot>: How many gallons are in the truck's tank? ** The truck tank has 10 gallons in it because 20 x .5 = <<20*.5=10>>10
How many gallons are in the car's tank? ** The car tank has 4 gallons in it because 12 x (1/3) = <<12*(1/3)=4>>4
How many gallons does she need to add to the truck? ** She needs to add 10 gallons to the truck because 20 - 10 = <<20-10=10>>10
How many gallons does she need to add to the car? ** She needs to add 8 gallons to the car because 12 - 4 = <<12-4=8>>8
How many gallons does she need to add in total? ** She needs to add 18 gallons in total because 10 + 8 = <<10+8=18>>18
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