substitution, 198
subtraction, 7
systems of equations, 197–206
tailwind, 140
time, 60, 131, 160
upstream, 140
whole numbers, 6–10
addition, 6
division, 8
multiplication, 8
subtraction, 7
total, 6, 8
word problems, 6–10
work backwards, 263–264
work problems, 62, 181–193INDEX 301