A coin whose faces are marked $$3$$ and $$5$$ is tossed $$4$$ times. The probability that the sum of the numbers thrown is greater than $$15$$ is

Question

Infinity Learn · Accepted Answer

let ' r ' denote the number of times $$3$$ appears $$n=4$$,$$r=0$$,$$1$$,$$2$$,$$3$$,$$4$$ 'P′ be the probability of a coin showing $$3$$⇒$$p=12$$,$$p+q=1$$⇒$$q=12Sum$$ is greater than $$15$$ At least $$2$$ coins show $$5At$$ most $$2$$ coins show $$3P0$$≤$$X=r$$≤$$2=PX=0+PX=1+PX=2$$      $$($$∵$$PX=r=nCrprqn$$−$$r)=4C0$$.$$P0$$.$$q4+4C1$$ .$$p1q3+4C2$$.$$p2q2=1241+4+6=1116$$

A coin whose faces are marked 3 and 5 is tossed 4 times. The probability that the sum of the numbers thrown is greater than 15 is

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