Float a div without defining height property

Question

It looks very simple (and maybe is, just got stucked) -> just for fun, no practical need right now.

I got this:

Answer 1

I think the best way is:

.master {
    width: 100%;
    height: 100%;
    display: table;
}
.left {
    width:10%;
    height: 100%;
    float: left;
    background: red;
    display: table;
}
.right {
    width: 89%;
    margin-left: 1%;
    float: left;
    background: blue;
    color: #FFF;
    display: table;
}