FX (simple): Money exchange for travel purposes

Wanted to start writing on my travel guide for Japan but I figured that many people just cannot understand FX (foreign exchange, it's just a big word for trading of currencies). For us layman's, we go to the money changer and get some foreign currency when we're travelling.
*Note: in many countries, an isolated store for money exchange is not common. People go to their banks, which we all know, give shit rates. Some others choose to exchange their money at the airport.
Whichever floats your boat, it's not my money.

So, here we go:

Remember in Secondary School when your textbook said "John has 5 SGD and the money change Mr. Muthu buys Euro @ 0.77 and sells Euro @ 0.67. How much Euros can John receive?"

             Buy       Sell
Euro     0.77       0.67

I can never forget how these questions were always racist but it's true that the indians are good with numbers. Anyway, here you go, 2 simple rules.
Remember,
1) the money changers are smart, they will always earn a margin.
2) you have to understand which currency is stronger & how are the denominations of things in that country. This principle don't change often so it's easy.

If you aren't sure which rate to use (BUY or SELL), consider the following scenarios where John changes 5 SGD into Euro and using that Euro, changing back into SGD on the SAME day with the SAME given rates.


Scenario A) Using 0.77 to change into Euro
Muthu takes the $5 and gives John 3.85 Euro (5*0.77).
John wants to change that back into SGD so Muthu will use 0.67 now and John gets $5.74.
Good deal for John!

Scenario B) Using 0.67 to change into Euro
Muthu takes the $5 and gives John 3.35 Euro (5*0.67).
John wants to change that back into SGD so Muthu will use 0.77 now and John gets $4.35.
Good deal for Muthu!

Simply, the money changer wants to earn so he's going to go with Scenario B.
And it's scenario B because when he gives John Euro, he is SELLING Euro --> 0.67 SGD to 1 Euro.

Some FX terms to help you understand the news:
appreciate = value goes higher --> 1USD = 60 yen
depreciate = value drops --> USD = 90 yen