For now, assume 4/5 and 45/100 are equal fractions
4/5 = 45/100
4*100 = 5*45 ... cross multiply
400 = 180
Since the left side (400) is larger than the right side (180), this means that the original left side (4/5) is larger than the original right side (45/100)
We can go back to the steps above and replace every equal sign with a "greater than sign" like so
4/5 > 45/100
4*100 > 5*45 ... cross multiply
400 > 180
the third inequality is true, which confirms the first inequality must also be true
Further confirmation can be found through using a calculator to convert to decimal form
4/5 = 0.80
45/100 = 0.45
We see that 0.80 is larger than 0.45, so 4/5 is larger than 45/100.