The average earning of each member of the Gates family is 20% less tha

Let's do the following notations:
#G - number of family members in Gates family
#B - number of family members in Buffet family
G - average earning of a Gates family member
B - average earning of a Buffet family member
TG - Total earnings Gates family
TB - Total earnings Buffet family

Thus, earning of the families are the following
TG = #G * G
TB = #B * B

we know
(1) "The average earning of each member of the Gates family is 20% less than the average earning of each member of the the Buffets family"=> G = B * 0.8#

(2) The total earning of the Gates family is 20% more than the total earning of buffets family""=> TG = 1.2 * TB

We are asked to find "the no. family members in the buffets family is what percent of the no.of the family members of gates:" => #B/#G

First let's plug in our total earnings equations into (2), we get:
#G * G = 1.2 * #B * B
Second step, we plug in (1) into this equations, we get:
#G * B * 0.8 = 1.2 * #B * B

We have to find #B/#G = (0.8 * B)/ (1.2 * B) = 0.8/1.2 = 0.66

Hope this helps.

I think one moderator should move this to the PS section.

We can let the average earning of each member of the Buffets family be 10, and thus the average earning of each member of the Gates family will then be 8. We can also let b = the number of members in Buffets family and g = the number of members in Gates family. Therefore, we can create the equation:

8g = 10b x 1.2

8g = 12b

b = 8g/12 = (2/3)g

We see that the number of members in Buffets family is ⅔, or 66.66%, of the number of members in Gates family.

Answer: A