A large circle has a radius of 10cm Given four congruent circles tangent to one another within the large circle what is the radius of the largest circle which will fit in the middle?

Letting x be radius of the 4 circles, then (squareroot(2x^2))+x=10, or x(1+sqrt2)=10.

Then radius of circle in middle is ((2*10)-4x)/2.

So I get radius of circle in middle = 1.715729 approximately.