By proportion. First write down the given information systematically:
[1000] drops of liquid equals (1 fl. oz.)
(100) drops of liquid equals ? oz
For problems that are directly proportional, we cross multiply the numbers in the bottom left and top right (in parentheses), divide by the number across ( in square brackets) from the unknown, namely:
Answer:
100 drops * 1 fl. oz / (1000 drops) = (100/1000)* 1 fl. oz = 0.1 fl. oz.
