Multiplying a number by 4/5 then dividing by 2/5 is the sames as multiplying by what number?

It is the same as multiplying by 2.

Step-by-step explanation:

Lets imagine that the number is one. In that case, you would have (1*4/5)/(2/5), which is the same thing as 4/5 divided by 2/5. from there you can solve this by using the keep change flip method.

You keep the first number, 4/5, change the operator to its opposite, from division to multiplication, and flip the final number, from 2/5 to 5/2. In the end, you end up with 4/5 * 5/2, which is equal to 2.

just sum

10 + 10 = 20