He made his mistake in Step 2. Tom should have subtracted 4/8 instead of 1/8. The mistake is that he was not consistent when he multiplied Denominators (bottom number) must be the same when handling fractions so Tom must multiply both the numerator and denominator by the SAME number to balance it out. 1/2 x 4/4= 4/8. Subtract. 7/8 - 4/8= 3/8. Tom has 3/8 of a gallon of paint leftover.
A two story home might use translation to have both floors identical and most homes have windows of the same size and shape so they might also use translation. Sometimes buildings use reflection to make rooms opposite each other the same.
