ACT Math : Compound Fractions

Example Questions

Example Question #451 : Arithmetic

John's shadow is six feet long, and Mary's shadow is five feet long. If John is four feet tall, which of the following is closest to Mary's height in inches?

Explanation:

First we set up a proportion. Mary's shadow (5 feet) to John's shadow (6 feet) is equal to Mary's height (x feet) to John's height (4 feet), i.e. 5 / 6 = x / 4.

Solve for x by first cross-mulitplying: 20 = 6x.

Divide both sides by 6: x = 20 / 6 feet

Multiply by 12 to find this height in inches: 20 * 12 / 6 = 20 * 2 = 40 inches

Example Question #1 : Compound Fractions

When two resistors ( and ) are added together in a parallel circuit to create an equivalent single resistor, the equivalent resistor () has a resistance defined by the following equation:

If  and , what does  equal?

None of the other answers

Explanation:

Plugging  and  into the equation gives:

Create a common denominator by multiplying  by  in the numerator and denominator:

Finally:

Example Question #453 : Arithmetic

What does  equal?