Can't you just weigh them by hand?
You should be able to tell which stack weighs 10 kilograms and which weighs 20 kilograms.
That way, you don't even have to use the scale. =P

I completely agree, the plot is so hard to predict in porn.

Anyway here's one.
Picture yourself in a bright beautiful sunny day, where the temperature is a comfortable warm that doesn't reach the point of being too hot. Few fluffy clouds cover the sky but there was one that stubbornly stopped right under the sun, thus creating a dim atmosphere. It's the kind of day that is perfect for picnics.

You we're driving home from work in your new smart car, surprisingly there was no traffic.
Not a single car in sight.
As you approached the bus station you regularly pass everday, something interesting caught your eye.
3 people were waiting for the bus.

One was a familiar face.
Your bestfriend from your childhood.
The type of friend you trusted with everything and even at one point saved your life.
Unfortunately, he had to move because of his parents job and you haven't seen nor spoke with him for more almost a decade.

The second face made your heart swoon.
It was something that you couldn't explain.
She/He was the love of your life.
She/He was your soulmate

The third face was tragic.
An old lady cringing in pain, crutching her heart.
It was obvious she needed quick medical attention and should be brought to the nearest medical facility

Now your smart car is very small and can only and only carry one passenger.
What do you do? 

 That's a no brainer:
1. Get your mates number so you can call him later to arrange a drinking session
2. Get the chick in the car
3. The world is full of old people so 1 less is neither here nor there.

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