Lisa and John are sister and brother. Lisa has as many brothers as sisters, and John has three times as many sisters as brothers. How many girls and boys are there in this family?

According to Lisa, her number of brothers and sisters is the same: B=S. This means that there is one more girls than boys: the amount of girls is Lisa + her sisters (imagine Lisa has 4 sisters and 4 brothers, than there are 5 girls and 4 boys). Thus, if G are the girls an B the boys:

G - 1 = B

According to John, the number of brothers is three times as many sisters as brothers. This implies that the number of brothers is the triple of the number of sisters. With B-1 being the number of John's brothers:

3 (B-1) = G

Resolving:

3( (G-1) -1 )=G

3(G-2)=G

3G - 6 = G

2G = 6

G=3

Replacing on our first equation:

B= 3 - 1

B=2

Answer: 3 girls and 2 boys

francocanacari francocanacari · Answer 2 · 2022-02-17T14:00:09+01:00

There are 3 girls and 2 boys in this family.

Logic

Given that Lisa and John are sister and brother, and Lisa has as many brothers as sisters, and John has three times as many sisters as brothers, to determine how many girls and boys are there in this family, the following calculation must be performed:

S = (B = S)
B = (3S =B)
Lisa = 1 B and 1 S = 3
John = 1 B and 3 S = 5
Lisa = 2 B and 2 S = 5
John = 1 B and 3 S = 5

Therefore, there are 3 girls and 2 boys in this family.

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