A company buys an equipment with $ 20. How it should be recorded in the books of Accounts? Is it a Debit in (A) Assets or (B) Expenses?

First if the equipement will last more than one year, Second, it depends on the company policy, if there is a scale for the aquisition price to record assets.

And20 USD doesn't seem to be a big amount of money, I would expense it , but , again it depends on the size and company  policy

As long as that equipment have probable future economic benefits and can be controlled by the entity, it should be recorded as asset. So letter A.

i think its an asset..

you'll debit asset and credit cash

 when you see principles of cost accounting you will find:

it depends on  time period for the company to benefit from the equipment

if it  less than one year>>>you can record it as expenses

if it more than one year>>>you can record it as assets

Do not look at the price but you must to  see the equipment benefit