Ratio and Proportion Flashcards

The ratio of the length to width of a rectangular electrical panel cover is 5:2. If the width is 14 inches, what is the length?

Answer: 35 inches

Using the proportion 5/2 = x/14 gives x = (5 × 14) / 2 = 35 inches.

An electrical plan calls for 3 outlets for every 150 square feet of floor space. How many outlets are needed for a 1,200 square foot area?

Answer: 24

The rate is 3 outlets per 150 sq ft, so for 1,200 sq ft: (1,200 / 150) × 3 = 8 × 3 = 24 outlets.

If the resistance of wire is directly proportional to its length, and 200 feet of wire has a resistance of 5 ohms, what is the resistance of 350 feet of the same wire?

Answer: 8.75 ohms

Setting up the proportion 5/200 = x/350 gives x = (5 × 350) / 200 = 8.75 ohms.

A union job requires 1 foreman for every 7 workers. If there are 56 workers on the site, how many foremen are required?

Answer: 8

Divide the number of workers by the ratio: 56 ÷ 7 = 8 foremen.

Materials for a job cost $420 and cover 280 square feet. How much will materials cost to cover 350 square feet at the same rate?

Answer: $525

The unit rate is $420 / 280 = $1.50 per sq ft; 350 × $1.50 = $525.

A conduit system uses a 4:1 ratio of horizontal runs to vertical runs. If there are 80 feet of horizontal conduit, how many total feet of conduit are in the system?

Answer: 100 feet

Horizontal is 4 parts, vertical is 1 part, so vertical = 80/4 = 20 feet; total = 80 + 20 = 100 feet.

A transformer steps voltage up in a 10:1 ratio. If the primary (input) coil has 500 turns and the secondary has 5,000 turns, and the input voltage is 120 volts, what is the output voltage?

Answer: 1,200 volts

The turns ratio is 5,000/500 = 10, so the output voltage is 120 × 10 = 1,200 volts.