Ashton Kutcher has swapped acting for maths lessons.

The 31-year-old actor has been struggling to relearn algebra so he can help his wife Demi Moore's 15-year-old daughter Tallulah with her homework.

Writing on his Twitter webpage, the 'Spread' star said: "Sometimes I think the only reason I took math is so I could help my kids take math.

"Assisting on some 10th grade math home work. BTW the absolute value of -4 is indeed 4. Now solving f(x)=-3lx-4l when x

Ashton isn't the only celebrity to struggle with their children's mathematics homework.

Soccer player David Beckham - who has three children, Brooklyn, 10, Romeo, seven, and four-year-old Cruz, with former Spice Girls singer Victoria Beckham - has previously admitted he is unable complete his sons' schoolwork.

He said: "Their homework is so hard these days. I sat down with Brooklyn the other day - and I was like, 'Victoria, maybe you should do the homework tonight'."