Your teeth. You get baby teeth and adult teeth as part of the life package, but once you lose those you get to pay for dentures (or scare small children with your sunken face).
Alfred is at the bank to cash his $200 check. He tells the cashier he would like some one dollar bills, ten times as many two dollar bills and the rest in fives.
How many of each denomination does the cashier need to give Alfred?
We know that in order to give the rest of the amount in fives, the sum of the one and two dollar bills needs to be divisible by five (i.e. end in 0 or 5).
If we start with a single one dollar bill, we’d need ten two dollar bills to satisfy the request, making $21. But we need a sum that is divisible by 5. So we keep going up, like so:
You are a spy and need to send an item to a contact in another country without letting anyone else have access to it. All unlocked items will be opened in transit. How can you send this item securely?
Place a lock on the item and send it to your contact. They will place their own lock on the package and return it to you. You remove your lock and send it back. When they receive it, they can unlock the package and retrieve the item.
It can’t be touched, but can be felt.
It can’t be opened, but can be gone into.
Those who seek it always find it under something,
yet it moves from place to place.
Shade. You can’t touch shade, but you can feel its coolness. You can’t open shade but you can go into it. If you’re looking for shade it always has to be underneath something to block the light and shade moves as the light does.
You ride on me every day but barely notice,
I’m hot and cold at the very same time,
I’m the densest of my clan,
And my first three help you enjoy music.
Earth. Most people don’t stop to think that they’re hurtling through space on a huge planet. At any given time the Earth has burning hot magma and freezing arctics at the same time. The Earth is the densest planet and the first three letters, “ear” help you listen to music.
I am pronounced as one letter but written as three,
There are two of me, I am single, I am double,
I can be blue, brown, black or green.
I can be read from right to left or left to right and am still the same.