secrets-of-mental-math-malestrom

Index 275
factoring a number:
in three-by-three multiplication,
181–83; exercises, 192–93;
answers, 265–68
in three-by-two multiplication,
169–72; exercises, 175–76;
answers, 259–62
in two-digit multiplication,
63–68; exercises, 68; answers,
243
Fibonacci numbers, xi
Fleischman, Martin, 228–29
fractions, 102–7
adding with equal denominators,
104–5; exercises, 105;
answers, 252
adding with unequal
denominators, 105–6;
exercises, 106; answers, 252
dividing, 103; exercises, 103;
answers, 252
multiplying, 102; exercises, 102;
answers, 252
one-digit, 93–96
simplifying, 96–97, 103–4;
exercises, 104; answers, 252
subtracting, 106–7; exercises,
107; answers, 252–53
friendly products, 66–68
Fuller, Thomas, 168
Gardner, Martin, 53–54
Gauss, Carl Friedrich, 20
Glois, Évariste, 121
Gold, Thomas, 228
Great Mental Calculators, The
(Smith), xxi
group theory, 121
guesstimation, 108–30
addition, 108–11; at the
supermarket, 111; exercises,
128; answers, 253
division, 112–14; exercises, 129;
answers, 254–55
multiplication, 114–17;
exercises, 129; answers,
254–55
sign for “approximately,” 109
square roots, 117–21; exercises,
130; answers, 255
subtraction, 111–12; exercises,
129; answers, 254
hearing numbers, 16
HIV-AIDS skeptics, 230
instant multiplication, 1–4
interest:
calculating, 125–28; exercises,
130; answers, 256
repaying a loan, 126–27
Rule of 70, 125–26
Rule of 110, 126
introspection illusion, 227
Kevles, Daniel, 227–28
Law of Large Numbers, 223
laws of probability, 224
leapfrog addition, 203–6
leap years, day of the week, 10,
220
left-to-right computations:
addition, 6–8, 11–21
division, 80
multiplication, 30–31, 33
subtraction, 6–7, 21–28
loan, repaying with interest,
126–27; exercises, 130;
answers, 256
logarithmic spirals, xi
magic squares, 206–9
how to construct, 207–8
why this trick works, 208–9
magic 1089, 200–202
math:
creative thinking in, xxiv
figuring out loud, xiv
as language of science, xi
useful language of, xvii
Mathemagics, xiii, xix, xxiii
“amazing” sum (Randi), 212–14
leapfrog addition, 203–6
magic squares, 206–9
magic 1089, 200–202