A triangle has a base length of 14 cm and a height of 10 cm. The base length increases

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[GMAT math practice question]

A triangle has a base length of 14 cm and a height of 10 cm. The base length increases by 10%, and the height decreases by 10%. What will the area of the triangle be?

A. Increases by 0.5 cm^2
B. Increases by 0.7 cm^2
C. Increases by 0.9 cm^2
D. Decreases by 0.3 cm^2
E. Decreases by 0.5 cm^2
Source: — Problem Solving |

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The area of the original triangle is (1/2)·14·10 = 70.

The area of the modified triangle is (1/2)·(14·(1 + 0.1))·(10·(1 - 0.1)) = (1/2)·14·10·(1 + 0.1)·(1 - 0.1) = 70·(1 - 0.01) = 70 – 0.7.
Thus, the area decreases by 0.7.
Therefore, B is the correct answer.
Answer: B