"if a japanese toy costs 20 yen and the yen per dollar exchange rate is 5, what is the dollar price of the japanese toy? "

The dollar price of the Japanese toy is: $ 4.

Exchange rate--

It the value of currency of one country in term's of the currency of the other country.

Here it is given that:

The yen per dollar exchange rate is 5.

This means that:

 5 yen= $ 1

This means that:

(5×4) yen=$ (1×4)

i.e.

20 yen=$ 4

Now the cost of Japanese toy is: 20 yen

Hence, the cost of the Japanese toy in dollars is: $ 4.