Question

80 is 4/5 of what number

Answer 1

its simple, first make 4/5 a decimal; 0.8

then multiply it by 80 cause of means multiplication;  80 × 0.8 = 64

So your final answer would be; 64

Answer 2

To find the answer to this, you first divide 80 by four to find what 1/5 is. 
80 divided by four is twenty, so 1/5=20.

20x5=100, so 80 is 4/5 of 100.

Hope I could help!