In sunlight, a vertical yardstick casts a 1 ft shadow at the same time that a nearby tree casts a 15 ft shadow. How tall is the tree? (Make a sketch to help solve the problem. Hint: 3ft equals one yard.)

The yardstick is 1 yard tall, which is 3 feet. At the same time of day, the yardstick and tree form similar triangles, so their height-to-shadow ratios are equal. The yardstick’s ratio is 3 feet to 1 foot, so a 15-foot tree shadow corresponds to a height of 3 × 15 = 45 feet. The tree is 45 feet tall, choice a.

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