Question

Difficulty: HardLinear Inequalities in One Variable

In the inequality 2(3xk)5(x+1)>17-2(3x - k) - 5(x + 1) > 17, kk is an integer constant. If the maximum integer value of xx that satisfies the inequality is 22, what is the least possible value of kk?

Answer: 23

Answer

The correct answer is 23.
By simplifying the inequality to x<2k2211x < \frac{2k - 22}{11}, we establish that the upper bound of the solution interval must be strictly greater than 22 but less than or equal to 33 for 22 to be the maximum integer solution. Solving the resulting compound inequality 2<2k221132 < \frac{2k - 22}{11} \le 3 yields 22<k27.522 < k \le 27.5. The smallest integer within this range is 2323.

Step-by-Step Solution

1
Distribute the constants on the left side of the inequality.
6x+2k5x5>17-6x + 2k - 5x - 5 > 17
Applying the distributive property simplifies the expression and removes the parentheses.
2
Combine like terms on the left side and isolate the xx term.
11x+2k5>17    11x>222k-11x + 2k - 5 > 17 \implies -11x > 22 - 2k
Grouping xx terms together and moving the constant terms to the other side prepares the inequality for division.
3
Divide both sides by 11-11 and flip the inequality sign.
x<222k11    x<2k2211x < \frac{22 - 2k}{-11} \implies x < \frac{2k - 22}{11}
Dividing by a negative number reverses the direction of the inequality sign from greater-than (>>) to less-than (<<).
4
Set up the inequality for the maximum integer solution to be 22.
2<2k221132 < \frac{2k - 22}{11} \le 3
For 22 to be the largest integer satisfying x<Lx < L (where LL is the boundary), 22 must be strictly less than LL, and LL must be less than or equal to the next integer, 33.
5
Solve the compound inequality for the parameter kk.
22<2k2233    44<2k55    22<k27.522 < 2k - 22 \le 33 \implies 44 < 2k \le 55 \implies 22 < k \le 27.5
Multiplying all parts by 11, adding 22, and dividing by 2 isolates kk.
6
Find the least integer value of kk in the interval (22,27.5](22, 27.5].
2323
The integers that satisfy 22<k27.522 < k \le 27.5 are 23,24,25,26,23, 24, 25, 26, and 2727. The least of these values is 2323.

Key Concept

Solving linear inequalities in one variable involving parameter bounds, negative coefficients, and integer solution constraints.
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