secrets-of-mental-math-malestrom

274
Index
close-together method:
of cubing, 77, 78
in multiplying three-by-three
numbers, 183–88; exercises,
192–93; answers, 265–68
Colburn, Zerah, 49, 53, 109
cold fusion debacle, 228–29
columns of numbers, adding (on
paper), 132–33; exercises,
149; answers, 256
complements, 25–28
confirmation bias, 224, 225, 229
conspiracy theories, 224
creationism, 229
criss-cross method of multiplication
on paper, 138–45; exercises,
150; answers, 257
cube roots, quick, 209–11
cubing:
close-together method, 77, 78
two-digit numbers, 76–79;
exercises, 79; answers, 248
data filters, 225–26
day of the week, 8–10, 214–21
day codes, 214–15
exercises, 221; answers, 270
Julian vs. Gregorian calendar, 220
leap years, 220
month codes, 215
year codes, 216–18
death premonitions, 223, 224
decimalization, 93–98; exercises,
98; answers, 250
Demon-Haunted World, The
(Sagan), 227
Devi, Shakuntala, 146
digital roots, checking solutions
via, 133
digits (fingers), xii
distributive law, 50–51
divisibility, testing for, 98–102
by 2, 99; exercises, 101;
answers, 250
by 3, 99; exercises, 101;
answers, 250
by 4, 99; exercises, 101;
answers, 250
by 5, 100; exercises, 101;
answers, 251
by 6, 100; exercises, 101;
answers, 250
by 7, 100; exercises, 102;
answers, 251
by 8, 99; exercises, 101;
answers, 250
by 9, 99; exercises, 101;
answers, 250–51
by 11, 100; exercises, 102;
answers, 251
any odd number not ending in 5,
100–101; exercises (by 17),
102; answers, 251
division, 80–107
decimalization, 93–98; exercises,
98; answers, 250
fractions, 103; exercises, 103;
answers, 252
guesstimation, 112–14;
exercises, 129; answers,
254–55
left to right, 80
numbers ending in 25 or 75,
97
one-digit numbers, 81–84;
exercises, 84; answers, 249
quotient in, 87
rule of “thumb” in, 84–86
as simplification process, 82
simplifying problems of, 90–93,
98
square root estimation, 117–21;
exercises, 130; answers, 255
square roots with pencil and
paper, 135–38; exercises, 150;
answers, 257
two-digit number into four-digit
number, 89–90
two-digit numbers, 87–93;
exercises, 93; answers, 249
when divisor ends in 5, 97
dreams, frequency of, 223
estimations, 12; see also
guesstimation
evolution, theory of, 229