Question

Susan has 3 lists, each with 10 numbers. If there are 4 numbers on all three lists and 5 numbers on exactly 2 lists, how many numbers belong to just one list?

Answer 1

Answer:

Susan has 8 numbers belonging to just one list.

Step-by-step explanation:

Susan's 3 lists have 10 numbers each = 10 x 3 =  30 numbers

4 numbers appear on all three lists = 4 x 3 = 12 numbers

The remaining numbers after these 12 = 18 (30 -12)

Then, there are 5 numbers on 2 lists only = 5 x 2 = 10 numbers

The numbers on just one list = 18 - 10 = 8 numbers

Or

                                    List 1     List 2    List 3   Total

Numbers on each list    10           10         10      30

Numbers on 3 lists        -4           -4         -4        12

Numbers on 2 lists        -5           -5        -0        10

Numbers on 1 list only    1             1          6         8