Answer:if the original question was
“Lisa has a bag of jelly beans. There are 8 red jelly beans in the bag, and the probability of drawing a red jelly bean out is 1/6. When she adds more red jelly beans to her bag, the probability becomes 1/5. How many red jelly beans did she add to the bag?”
Which I had done in my shsat work.
The answer is 2.
To find this:
You do trail and error.
Probability is favored outcome/total outcome.
Since 8 is the favored outcome for the first part,being 1/6 of the total outcome. You can multiply to 6 to get the total, or 48.
You are only increasing the red jelly beans, keep in mind you add one to the favored outcome as well as the total.
8+1/48+1=9/49
The probability of 9/49 is 0.18367346938, close to 0.18 (18/100) but not 1/5 (0.2) IN EXACT. For shsat, you can’t use calculator I think so you can just simplify down if both the denominator and numerator are multiples of 5.
Continuing on, with 10/50, it would be simplified to 0.2 or 1/5 and it has the right probability.
However, for this question we are solving for number of added jelly beans, so we need to subtract 8(original) from 10(total after adding), which will be 2 jelly beans. I know this post was from last year but I just saw it and feel like answering. Happy new year!
