You started with 32 muffins.
[tex] \frac{20 \: muffins}{total \: muffins} = \frac{5}{8} [/tex]
You can use either cross multiplication
[tex]5 \times (total \: muffins) = 8 \times 20 \: muffins \\ 5x = 160 \\ x = 160 \div 5 = 32 \: total \: muffins[/tex]
You can also show that you can get to 20 muffins by multiplying 5 by 4. In order to keep the fraction equal, you would also have to multiply 8 × 4 = 32 total muffins.
