Aseven-digit phone number in the united states consists of a three-digit exchange followed by a four-digit number. a. the first digit of the exchange is not allowed to be a zero or a one. how many seven-digit numbers can be formed?

solution:

→c= a b , that is product of a and b is possible only when when a is m × n matrix and b is n × p matrix.

that is, number of columns of a= number of rows of b.

so, size of matrix , c= a b is , if a = (m × n)matrix

b= (n × p)matrix

then a b = [ (m × n)matrix] ×[   (n × p)matrix ]

→→c= a b= [m × p ] matrix

→→size of product a b will be equal to = number of rows of a × number of columns of b

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step-by-step explanation:

i wish i could u