Puzzle Details

Daniel has twice as many sisters as brothers.

His sister, Jessica, has one more sister than she has brothers.

How many boys and girls are there in the family?

Answer: There are four boys and six girls in the family.

If there were B boys, and G girls we know that Daniel has twice as many sisters as brothers, so 2 x (b - 1) = g.

And his sister, Jessica, has one more sister than she has brothers, so g - 1 = b + 1.

2(b - 1) = g       [1]
g - 1 = b + 1   [2]

Using [1] in [2] gives:

2(b - 1) - 1 = b + 1

Expanding the bracket gives:

2b - 2 - 1 = b + 1

Simplifying the left hand side gives:

2b - 3  = b + 1

Add 3 to each side gives:

2b = b + 4

Subtract b from both sides gives:

b = 4

Using b = 4 in [1] gives:

2(4 - 1) = g

6 = g

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