The truck tank has 10 gallons in it because 20 x .5 = <<20*.5=10>>10

The car tank has 4 gallons in it because 12 x (1/3) = <<12*(1/3)=4>>4

She needs to add 10 gallons to the truck because 20 - 10 = <<20-10=10>>10

She needs to add 8 gallons to the car because 12 - 4 = <<12-4=8>>8

She needs to add 18 gallons in total because 10 + 8 = <<10+8=18>>18

# Answer

18
<|im_start|>system
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<|im_start|>user
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?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
18
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?
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