How many hours (to the nearest hour) would it take you to count one billion if you counted one number every twenty seconds?
hint 1
Three numbers could be counted in a minute. Similarly, try to find the count for an hour.
hint2
If 180 numbers are counted in one hour, one billion numbers can be counted in how many hours?

You would need 5,555,556 hours to count 1 billion.

Step-by-step explanation:

Proportions

If you count one number every 20 seconds, then you can count 3 numbers in a minute.

Counting 3 numbers in a minute will allow counting 3*60 = 180 numbers in an hour.

At the same counting rate, if you wanted to count 1 billion numbers, we can calculate the hours needed by dividing:

1,000,000,000 / 180 = 5,555,555.55

Rounding to the nearest hour, you would need 5,555,556 hours to count 1 billion.