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Let N = (10^143 -1)/9 Then which of the ...

Let `N = (10^143 -1)/9` Then which of the following is true?

A

N is prime

B

` N = (1+10^(12) + 10^(24) + …+10^(132))(1+10 + 10^(2) +…+10^(10))`

C

` N = (1+10^(11) + 10^(22) + …+10^(132))(1+10 + 10^(2) +…+10^(10))`

D

` N = (1+10^(13) + 10^(26) + …+10^(130))(1+10 + 10^(2) +…+10^(12))`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we start with the expression given for \( N \): \[ N = \frac{10^{143} - 1}{9} \] ### Step 1: Understanding the Expression The expression \( 10^{143} - 1 \) can be interpreted as a number that consists of 143 nines. This is because \( 10^{143} \) is a 1 followed by 143 zeros, and subtracting 1 from it gives us 143 nines. ### Step 2: Simplifying \( N \) Now, we can rewrite \( N \): \[ N = \frac{999\ldots9}{9} \] where there are 143 nines in the numerator. Dividing each 9 by 9 gives us: \[ N = 111\ldots1 \] where there are 143 ones in the result. ### Step 3: Analyzing the Value of \( N \) The number \( N \) can be expressed as: \[ N = 111\ldots1 \quad (\text{143 times}) \] This number can also be represented in terms of powers of 10: \[ N = 1 + 10 + 10^2 + \ldots + 10^{142} \] This is a geometric series with the first term \( a = 1 \) and the common ratio \( r = 10 \). The formula for the sum of a geometric series is: \[ S_n = \frac{a(r^n - 1)}{r - 1} \] where \( n \) is the number of terms. Here, \( n = 143 \): \[ N = \frac{1(10^{143} - 1)}{10 - 1} = \frac{10^{143} - 1}{9} \] This confirms our earlier expression for \( N \). ### Step 4: Checking the Options 1. **Option 1: Is \( N \) prime?** - \( N \) is a repunit (a number consisting solely of the digit 1). A repunit \( R_k \) is prime only if \( k \) is prime. Since \( 143 = 11 \times 13 \), \( N \) is not prime. 2. **Option 2: \( N = 1 + 10^{12} + 10^{24} + \ldots + 10^{32} \)** - This expression does not correctly represent \( N \) because it does not yield the correct number of ones. 3. **Option 3: \( N = 1 + 10^{10} + 10^{20} + \ldots + 10^{132} \)** - This expression also does not yield the correct number of ones. 4. **Option 4: \( N = 1 + 10^{11} + 10^{22} + \ldots + 10^{133} \)** - This expression does not yield the correct number of ones either. ### Conclusion From the analysis, we find that: - **Option 1 is false** (N is not prime). - **Options 2, 3, and 4 are also false** as they do not correctly represent \( N \). Thus, the correct conclusion is that none of the options provided are true.
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