There are 10 history books in a bookcase. When the number of books increases by x percent, the new number of history books is 24. What is the value of x?

Explanation

To solve this problem, use the formula for percentage increase: new number = original number × (1 + x/100). Here, the original number of history books is 10, and the new number is 24. Set up the equation:24 = 10 × (1 + x/100)Divide both sides by 10 to isolate the percentage increase:2.4 = 1 + x/100Subtract 1 from both sides:1.4 = x/100Multiply both sides by 100 to solve for x:x = 140Therefore, the correct answer is Option D: 140. This means the number of books increased by 140%, making Option D correct. The other options (58, 70, and 120) do not satisfy the equation, as shown in their respective explanations.