Brego wrote:
ScottTargetTestPrepHey Scott,
I was wondering why formula given in
TTP formula sheet won't work: Unique members = All A + All B + All C - Groups of two - 2 group of three + Neither.
If I plug in I find that Neither is 71.
I solved all
ttp questions and didn't get anything like this
75 = 48 + 45 + 58 - (28 +37 +40) - 2(25) + Neither
I also see this formula being cited:Total=A+B+C−(sum of 2−group overlaps)+(all three)+Neither
I haven't seen this formula on
TTP either
Thank you
I understand that some of the quantities in the formula need clarification. For instance, in the formula:
Unique members = All A + All B + All C - Groups of two - 2 group of three + Neither
“Groups of two” refers to the number of members who belong to exactly two of the groups. For instance, in the question it says 28 people like pizza and hoagies; however, the 28 people also include people who like pizza, hoagies AND tacos. For the formula to work, you need to take the number of people who like ONLY pizza and hoagies to be 28 - 25 = 3. Similarly for the remaining groups of two.
If you take the number of unique members to be 75; All A, All B and All C to be 48, 45 and 58 respectively; groups of two to be 30 (because there are 28 - 25 = 3 who like pizza and hoagies only, 37 - 25 = 12 who like pizza and taco only, 40 - 25 = 15 who like pizza and taco only, for a total of 3 + 12 + 15 = 30) and groups of 3 to be 25; you’ll get:
75 = (48 + 45 + 58) - 30 - 2(25) + neither
75 = 151 - 30 - 50 + neither
neither = 4
By the way, if you solve 75 = 48 + 45 + 58 - (28 +37 +40) - 2(25) + Neither; you’ll get neither = 79, not 71.
If you’d rather use the formula Total=A+B+C−(sum of 2−group overlaps)+(all three)+Neither, then you need to take 48 + 45 + 58 = 105 for the quantity “sum of 2-group overlaps”.
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