comment calcul t-on ça!!!

Bonsoir Abdellehius

[tex]C_2^{40}\times0,05^2\times0,95^{38}=\dfrac{40\times39}{2}\times0,05^2\times0,95^{38}\\\\C_2^{40}\times0,05^2\times0,95^{38}\approx780\times0,0025\times0,1423957413\\\\\boxed{C_2^{40}\times0,05^2\times0,95^{38}\approx0,28}[/tex]