You were very close, what you need is not to work with decimal numbers as min and max. Let's have max = 1000 and min = 100, so after your Math.floor you will need to divide by 100:

var randomnum = Math.floor(Math.random() * (1000 - 100) + 100) / 100;

Or if you want to work with decimals:

var precision = 100; // 2 decimals
var randomnum = Math.floor(Math.random() * (10 * precision - 1 * precision) + 1 * precision) / (1*precision);

I can't find a dupetarget for this, so:

You do what John Coleman said: You generate a random number between 6000 and 6500:

var num = Math.floor(Math.random() * 500) + 6000;

...and divide by 100:

var num = (Math.floor(Math.random() * 500) + 6000) / 100;
// New bit ---------------------------------------^^^^^^

That gives you a number from 60 (inclusive) to 65 (exclusive) with a fractional portion that will in theory be roughly two digits, but because of the way IEEE-754 double-precision binary floating point (the kind of numbers JavaScript uses) works, if you output that, you may get more or fewer digits right of the decimal.

To output it with two digits, you use toFixed(2):

console.log(num.toFixed(2));

Example:

var counter = 0;
tick();
function tick() {
    var num = (Math.floor(Math.random() * 500) + 6000) / 100;
    console.log(num.toFixed(2));
    if (counter++ < 100) {
        setTimeout(tick, 250);
    }
}

.as-console-wrapper {
  max-height: 100% !important;
}

If you want the random numbers with 0.1 steps, the easiest would be to generate a random number between 1 and 15, then divide the result by 10.

(Math.floor(Math.random() * 15) + 1) / 10;