Explain how to find 40 x 50 using mental math

During a bike challenge riders have to collect various colored ribbons each 1/2 mile they collect a red ribbon each eighth mile they collect a green ribbon and each quarter mile they collect a blue ribbion wich colors of ribion will be collected at the 3/4 markrer

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Idon't want to fail summer school.the probabilities of contamination in medicine capsules due to the presence of heavy metals and different types of microbes are given in the table.the probability of capsule b having microbial contamination is (the same as, greater than, less than) the probability of capsule d having it.