Question

The number 0.4 can written as 4/10, so it is a rational number

Answer 1

Yes because rational numbers can be turned into a fraction and as you see that's what you did...

0.4=4/10

Your answer is yes it is a rational number.

Answer 2

True

An easy way to tell if a number is irrational if you cannot count it, or convert it into a decimal/fraction.

Such as pie, square root of 11, etc.