Practise Rachel's method for finding percentages and you'll know if you've got a real bargain on your hands in no time. Check out another double-digit multiplication trick with Rachel's maths hack ...

Now we know one percent of the dinosaur's length we can just multiply that by 12 to find 12%. Then we'll know how long the little one is. 3cm multiplied by 12 is 36cm. The trick is to keep it ...