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.
Well, there are different ways to do this if you are really familiar with fractions, but "officially" :P
1) convert mixed numbers to improper fractions.
rule: a b/c = (ac+b)/c
2) make all fractions have a common denominator...
a/b+c/d
(a/b)(d/d)+(c/d)(b/b)
(ad/bd)+(cb/bd)
3)
The simplify your final answer with greatest common denominator or convert back to mixed number if needed...
Like earlier take the bigger shape and divide the smaller one.
8.4 divide by 4 and you get 2.1.
3/8ths or 0.375 probability
