Answer: he has thirty $10 coin and sixteen $20 coin.
Step-by-step explanation:
Let x represent the number of $10 coin that he has.
Let y represent the number of $20 coin that he has.
He has a collection of 46 coins. Some are $10 coins and the rest ate $20 coins. This is expressed as
x + y = 46
If the face value of the coins is $620, it means that
10x + 20y = 620 - - - - - - - - - - - -1
Substituting x = 46 - y into equation 1, it becomes
10(46 - y) + 20y = 620
460 - 10y + 20y = 620
- 10y + 20y = 620 - 460
10y = 160
y = 160/10 = 16
x = 46 - y = 46 - 16
x = 30
