Answer: 12 red balls must be added
Step-by-step explanation:
Starting out with 15 balls, 6 red implies 9 blue. If blue remains 9, then we expect red to be 18 for a probability at 2/3. 18-6 = 12
We can use ratios and the cross-multiply-divide to find this.
The ratio 21:5 is avaliable via the question. We then need to compare that to the ratio x:100, the 100 being the percent and the x being the number of airplane parts.
21/5 = x/100
We can then solve for x to find the number of airplane parts. First we multiply by 100 on both sides to get 2100/5 = x. Therefore x = 420 and there are 420 airplane parts.
