13+(3+7)=(13+3)+7 what property is that

Three coins are flipped. what is the probability that there will be at least two tails?

Successful implementation of a new system is based on three independent modules. module 1 works properly with probability 0.96. for modules 2 and 3, these probabilities equal 0.95 and 0.90. compute the probability that at least one of these three modules fails to work properly.

In what organelle does photosynthesis take place?