Answer:
2 gallons
Step-by-step explanation:
The radiator contains 4 gallons of a 25% solution.
There are [tex]4\cdot 0.25=1[/tex] gallon of antifreeze in these 4 gallons.
Let x gallons of antifreeze is the amount of antifreeze that should be added, then
[tex]1+x \ - \ 50\%\ [\text{Amount of antifreeze}]\\ \\4+x\ -\ 100\%\ [\text{Total amount}][/tex]
Write a proportion:
[tex]\dfrac{1+x}{4+x}=\dfrac{50}{100}[/tex]
Cross multiply:
[tex]100(1+x)=50(4+x)\\ \\100+100x=200+50x\\ \\100x-50x=200-100\\ \\50x=100\\ \\x=2[/tex]
