1.

The total number not more than 20 digits that areformed by usingd the digits 0, 1, 2, 3, and 4 isa. `5^(20)`b. `5^(20)-1`c. `5^(20)+1`d.none of theseA. `5^(20)`B. `5^(20)-1`C. `5^(20)+1`D. none of these

Answer» We have,
Number of numbers
`=sum_(r=1)^(20)` (No. of r digit numbers)
`=5+4.5+4.5^(2)+4.5^(3)+......+4.5^(19`
`=5+4xx5((5^(19)-1)/(5-1))=5+5^(30)-5=5^(20)`
ALITER Number of numbers `=sum_(r=1)^(20)` (N0. of r digit numbers)
`=5+sum_(r=1)^(20)4xx5^(r-1)`


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