Practice questions
In the following questions, solve for x in each case just by looking at the equation.1. 18 – x = 12
2. 4x = 44
In the following questions, use the correct inverse operation to rewrite and solve each problem.
3. 100 – x = 58
4. 238/x = 17
In the following questions, find the value of x in each equation by guessing and checking.
5. 12x – 17 = 151
6. 19x – 8 = 600
Answers and explanations
- x = 6You can solve this problem through simple inspection. Because 18 – 6 = 12, x = 6.
- x = 11Again, through simple inspection, because 4(11) = 44, you know that x = 11.
- x = 42Turn the problem around by changing the subtraction to addition: 100 – x = 58 means the same thing as 100 – 58 = x, so x = 42.
- x = 14Turn the problem around by switching around the division:
so x = 14.
- x = 14Guess what you think the answer may be. For example, perhaps it's x = 10:
12(10) – 17 = 120 – 17 = 103
103 is less than 151, so this guess is too low. Try x = 20:
12(20) – 17 = 240 – 17 = 223
223 is greater than 151, so this guess is too high. Therefore, x is between 10 and 20. Try x = 15:
12(15) – 17 = 180 – 17 = 163
163 is a little greater than 151, so this guess is a little too high. Try x = 14:
12(14) – 17 = 168 – 17 = 151
151 is correct, so x = 14.
- x = 32Again, start by guessing. First, try x = 10:
19(10) – 8 = 190 – 8 = 182
182 is much less than 600, so this guess is much too low. Try x = 30:
19(30) – 8 = 570 – 8 = 562
562 is still less than 600, so this guess is still too low. Try x = 35:
19(35) – 8 = 665 – 8 = 657
657 is greater than 600, so this guess is too high. Therefore, x is between 30 and 35. Try x = 32:
19(32) – 8 = 608 – 8 = 600
600 is correct, so x = 32.