In a bag there are 90 red counters. the probability is 0.3. how many blue counters?

To find the number of blue counters, we first determine the total number of counters in the bag. Given that the probability of selecting a red counter is 0.3 and there are 90 red counters, we can use the formula for probability: ( P(\text{Red}) = \frac{\text{Number of Red Counters}}{\text{Total Counters}} ). Rearranging, we find that the total number of counters is ( \frac{90}{0.3} = 300 ). Thus, the number of blue counters is ( 300 - 90 = 210 ).