Question

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

Answer 1

4 boys, 3 girls

Explanation:

brothers of John ⇒ x

sisters of John ⇒ y

John has as many brothers as sisters:

1. x = y

brothers of Emily ⇒ x + 1 (Emily have the same amount of brother as John, plus one (John))

sisters of Emily ⇒ y -1 (Emily have the same amount of sister as John, minus one (herself))

Emily has twice as many brothers as sisters:

1. 2 (y-1) = x+ 1

Now we have a system of 2 equations and 2 variables

x=y (I)

2y - 2 = x + 1 (II)

____________

Replace x in equation II

2y - 2 = y + 1

2y - y = 2 + 1

y = 3

____________

Replace y in equation I

x = y = 3

That mean that John have 3 brothers plus himself, there is 4 boys in the family and John have 3 sister, so there is 3 girls in the family