For this case what you need to know is that each package contains 2 balloons.
Therefore, you can solve the problem by making the following rule of three:
1 package ---> 2 balloons
x ---------------> 275 balloons
Clearing x we have:
x = (275/2) * (1)
x = 137.5
Nearest whole number:
x = 138
Answer:
I need to buy 138 packs of balloons
