Question Details

Let m and n be natural numbers such that n is even and 0.2<m20,nm,n11<0.5. Then m2n equals

Options

A

3

B

4

C

1

D

2

Show Answer

Correct Answer :

Option C

1

Solution :

The correct option is 1.

To find the value of m&#x2212;2n, we need to determine the natural numbers m and n that satisfy the given conditions.
We are given that n is an even natural number and that the following three inequalities hold simultaneously:
0.2 &lt; m 20 &lt; 0.5
0.2 &lt; n 11 &lt; 0.5
0.2 &lt; n m &lt; 0.5

Step 1: Solve for the range of m from the first inequality
Multiplying the inequality 0.2&lt;m20&lt;0.5 by 20, we get:
20 &#x00D7; 0.2 &lt; m &lt; 20 &#x00D7; 0.5
4 &lt; m &lt; 10
Since m is a natural number, m must belong to the set:
m &#x2208; { 5 , 6 , 7 , 8 , 9 }

Step 2: Solve for n from the third inequality and given conditions
Multiplying the inequality 0.2&lt;n11&lt;0.5 by 11, we get:
11 &#x00D7; 0.2 &lt; n &lt; 11 &#x00D7; 0.5
2.2 &lt; n &lt; 5.5
Since n is given to be an even natural number, the only even integer in this range is 4.
Therefore, we have:
n = 4

Step 3: Solve for m using the middle inequality
Substituting n=4 into 0.2&lt;nm&lt;0.5, we get:
0.2 &lt; 4 m &lt; 0.5
Taking the reciprocal of all terms and reversing the inequalities yields:
1 0.5 &lt; m 4 &lt; 1 0.2
Simplifying the fractions:
2 &lt; m 4 &lt; 5
Multiplying by 4:
8 &lt; m &lt; 20

Step 4: Find the unique value for m and calculate the expression
Combining the constraints from Step 1 (4&lt;m&lt;10) and Step 3 (8&lt;m&lt;20), we get the intersection:
8 &lt; m &lt; 10
Since m is a natural number, the only integer satisfying this condition is:
m = 9
Finally, we compute m&#x2212;2n:
m &#x2212; 2 n = 9 &#x2212; 2 ( 4 ) = 9 &#x2212; 8 = 1

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