Can you solve it? We are (puzzle) family

Photograph: Harry Langdon/Getty Images

It’s March, so let’s begin with this riddle:

1. The two sisters

Twin girls are born in March, they celebrate their birthdays in September, when they grow up they marry each other.

Explain, please.

And, in honour of Sister Sledge, I ask: Are you the greatest solver?

2. The four sisters

A mother with four daughters sews a flag in the shape of an irregular quadrilateral, which she divides by the two diagonals into four different coloured triangles, as shown below.

The areas of the triangles (in square inches) correspond exactly to the ages of the four daughters. The elder sisters are two, six and twelve years older than the youngest.

What are the ages of the daughters?

This puzzle is a lovely twist on the genre of puzzles that always asks ‘what are the ages of the children?’ At first, it appears that you have far too little information to work out the answer, but it can be deduced with some simple geometrical observations. The only technical knowledge required is the formula that the area of a triangle is half the base times the height. (An irregular quadrilateral just means that the sides and angles are not all the same, as they are in, say, a square.)

I’ll be back at 5pm with the solutions. Meanwhile NO SPOILERS, please! Instead discuss your favourite all-sibling bands.

I set a puzzle here every two weeks on a Monday. I’m always on the look-out for great puzzles. If you would like to suggest one, email me.

I’m the author of several books of puzzles, most recently the Language Lover’s Puzzle Book.

Thanks to Chris Sealey for the ‘two sisters’ riddle, and to Manfred Pietsch for the ‘four sisters’ puzzle.