It is very likely that your question has an error.

Maybe you can change the ⅓ to ½ instead.


Concept : equal fractions (numerator)

Make the units the same by changing the numerator to the same number.

For gold, 1/2 = 2/4

For silver, we can leave it as 2/5

So we can now say that:

There were 4 units of gold balloons and 2 units were used.

There were 5 units of silver balloons and 2 units were used.

Total balloons = 4 units + 5 units = 9 units

9 units = 72 balloons
1 unit = 72 balloons ÷ 9 = 8 balloons

Number of balloons used = 2 units × 2
= 4 units
= 4 × 8
= 32

Alternatively, use 77 instead of 72.

Concept : equal fractions (numerator)

Make the units the same by changing the numerator to the same number.

For gold, 1/3 = 2/6
For silver, we can leave it as 2/5

So we can now say that:

There were 6 units of gold balloons and 2 units were used.

There were 5 units of silver balloons and 2 units were used.

Total balloons = 6 units + 5 units = 11 units


11 units = 77 balloons
1 unit = 77 balloons ÷ 11 = 7 balloons

Number of balloons used = 2 units × 2
= 4 units
= 4 × 7
= 28

Consult the teacher in school when you have the opportunity. Very certain the question has erroneous values.