Baseball Batting Average

A baseball player's batting average is calculated by the following formula:

BA = (number of hits) / (number of official at-bats)

Batting averages are always expressed rounded to the nearest thousandth with no leading zero. The top 3 MLB batting averages of all-time are:

1. Ty Cobb .366
2. Rogers Hornsby .358
3. Shoeless Joe Jackson .356

The given list represents a season of games. Each list item indicates a player's [hits, official at bats] per game. Return a string with the player's seasonal batting average rounded to the nearest thousandth.

Examples

batting_avg([[0, 0], [1, 3], [2, 2], [0, 4], [1, 5]]) ➞ ".286"

batting_avg([[2, 5], [2, 3], [0, 3], [1, 5], [2, 4]]) ➞ ".350"

batting_avg([[2, 3], [1, 5], [2, 4], [1, 5], [0, 5]]) ➞ ".273"

Notes

• The number of hits will not exceed the number of official at-bats.
• The list includes official at-bats only. No other plate-appearances (walks, hit-by-pitches, sacrifices, etc.) are included in the list.
• HINT: Think in terms of total hits and total at-bats.