8 Math for Automotive Technicians Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website. In these basic subtraction examples, 8 minus 2 equals 6. The problem can be written vertically or horizontally, as shown. Generally, the vertical format is easier to solve, and will be useful when the number values are larger. 8 – 2 8 – 2 = 6 6 Complete subtraction practice problems 2.1. Subtraction problems with larger minuend and subtrahend values may require borrowing value from the next column in order to complete the operation. Review the examples. 11 2 17 3 1 11 3 7 4 2 1 – 1 9 – 2 8 9 1 8 1 3 2 Complete subtraction practice problems 2.2. Subtraction problems may result in a difference that is a negative number. This occurs when a larger number is subtracted from a smaller number. To calculate these problems, subtract the smaller number from the larger number, and then use the sign (+ or –) of the larger number for the answer. Review the examples. 4 5 – 9 – 1 5 – 5 – 1 0 Complete subtraction practice problems 2.3. Subtraction problems may also be presented as word problems. This type of math problem requires reading through a written problem and extracting the critical information required to solve the problem. Example: An auto repair shop earns a promotional rebate from an auto parts supplier once they replace 20 sets of brake pads. So far they have re- placed 9 sets of brake pads. Calculate how many more sets of brake pads must be replaced to earn the promotional rebate. brake pad set replacements – brake pad = remaining brake needed for rebate sets replaced pad sets 20 brake pad sets – 9 brake pad sets = 11 brake pad sets 11 more sets of brake pads need to be replaced. Often, word problems will include distracting information that is not part of the math operation needed to solve the problem. Notice in the following example that the engine size information is not part of the math problem, and is distracting information. Review the example. Example: A technician is performing a compression test on a 3.8-liter V6 engine. The lowest cylinder has a compression of 129 psi and the highest cylinder has a compression of 145 psi. Calculate the difference between the highest and lowest cylinders. compression in highest cylinder – compression in lowest cylinder = difference 145 psi – 129 psi = 16 psi 16 psi is the difference between the highest and lowest cylinders. Complete subtraction practice problems 2.4.