Step-by-step explanation:
a probability is always desired cases / total cases.
from the table and given information we know :
there are 40 blue counters.
0.25 = 40/x
x being the total number of counters in the box.
x = 40 / 0.25 = 160
the sum of all probabilities must be 1 (the always true probability), as there are only counters in the box, and one of the 4 colors is always the result.
so,
1 = 0.25 + 0.35 + 0.3 + red-probability
1 = 0.9 + red-probability
red-probability = 1 - 0.9 = 0.1
0.1 = red counters / 160
red counters = 0.1 × 160 = 16
there are 16 red counters in the box.
