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From B. Lee Clay


 Squaring Numbers

 Multiplying Numbers

  1. same 1st digit
  2. same 1st digit, sum 10
  3. same 2nd digit
  4. 3 digits, middle 0
  5. 3 digits, middle 1
  6. 3 digits, middle 2
  7. 3 digits, middle 3
  8. 3 digits, middle 4
  9. 3 digits, middle 5
  10. difference of 1
  11. difference of 2
  12. difference of 3
  13. difference of 4
  14. difference of 6
  15. difference of 8
  16. difference of 10
  17. 2 digits by 1 1/25
  18. 2 digits by 1 1/16
  19. 2 digits by 1 1/15
  20. 2 digits by 1.1
  21. 2 digits by 1 1/9
  22. 2 digits by 1 1/8
  23. 2 digits by 1 1/7
  24. 2 digits by 1 1/6
  25. 2 digits by 1 1/5
  26. 2 digits by 1 2/9
  27. 2 digits by 1 1/4
  28. 2 digits by 1 2/7
  29. 2 digits by 1.3
  30. 2 digits by 1 1/3
  31. 2 digits by 1 3/8
  32. 2 digits by 1 2/5
  33. 2 digits by 1 3/7
  34. 2 digits by 1 1/2
  35. 2 digits by 1 4/7
  36. 2 digits by 1 3/5
  37. 2 digits by 1.6
  38. 2,3 digits by 1 2/3
  39. 2 digits by 1.7
  40. 2 digits by 1 5/7
  41. 2 digits by 1 3/4
  42. 2 digits by 1 4/5
  43. 2 digits by 1 5/6
  44. 2 digits by 1 6/7
  45. 2 digits by 1.9
  46. 2 digits by 2.1
  47. 2 digits by 2 1/9
  48. 2 digits by 2 1/7
  49. 2 digits by 2 1/5
  50. 2 digits by 2 2/9
  51. 2 digits by 2 1/4
  52. 2 digits by 2.3
  53. 2 digits by 2 1/3
  54. 2 digits by 2 3/8
  55. 2 digits by 2 2/5
  56. 2 digits by 2.4
  57. 2 digits by 2 4/9
  58. 2, 3 digits by 2 1/2
  59. 2 digits by 2 4/7
  60. 2 digits by 2.6
  61. 2 digits by 2 5/8
  62. 2 digits by 2 2/3
  63. 2 digits by 2.7
  64. 2 digits by 2 5/7
  65. 2 digits by 2 3/4
  66. 2 digits by 2.8
  67. 2 digits by 2 7/9
  68. 2 digits by 2 6/7
  69. 2 digits by 2.9
  70. 2 digits by 3.1
  71. 2 digits by 3 1/8
  72. 2 digits by 3 1/7
  73. 2 digits by 3 1/6
  74. 2 digits by 3.2
  75. 2 digits by 3 2/9
  76. 2 digits by 3 1/4
  77. 2 digits by 3 1/3
  78. 2 digits by 3.4
  79. 2 digits by 3 3/7
  80. 2 digits by 3 4/9
  81. 2 digits by 3 1/2
  82. 2 digits by 3.6
  83. 2 digits by 3 4/7
  84. 2 digits by 3 5/8
  85. 2 digits by 3 2/3
  86. 2 digits by 3.7
  87. 2 digits by 3 5/7
  88. 2 digits by 3 3/4
  89. 2 digits by 3 4/5
  90. 2 digits by 3 6/7
  91. 2 digits by 3 7/8
  92. 2 digits by 3.9
  93. 2 digits by 4.1
  94. 2 digits by 4 1/4
  95. 2 digits by 4 1/7
  96. 2 digits by 4 1/6
  97. 2 digits by 4 1/5
  98. 2 digits by 4 2/7
  99. 2 digits by 4 1/3
  100. 2 digits by 4.3
  101. 2 digits by 4.4
  102. 2 digits by 4 3/7
  103. 2 digits by 4 4/9
  104. 2 digits by 4 1/2
  105. 2 digits by 4 5/9
  106. 2 digits by 4.6
  107. 2 digits by 4 2/3
  108. 2 digits by 4.7
  109. 2 digits by 4 3/4
  110. 2 digits by 4 4/5
  111. 2 digits by 4 5/6
  112. 2 digits by 4 7/8
  113. 2 digits by 4.9
  114. 2 digits by 5.1
  115. 2 digits by 5 1/8
  116. 2 digits by 5 1/6
  117. 2 digits by 5.2
  118. 2 digits by 5 1/4
  119. 2 digits by 5.3
  120. 2 digits by 5 4/9
  121. 2 digits by 5 1/2
  122. 2 digits by 5 5/9
  123. 2 digits by 5.6
  124. 2 digits by 5.7
  125. 2 digits by 5 4/7
  126. 2 digits by 5 5/7
  127. 2 digits by 5 4/5
  128. 2 digits by 5 6/7
  129. 2 digits by 5.9
  130. 2 digits by 6.1
  131. 2 digits by 6 1/8
  132. 2 digits by 6 1/5
  133. 2 digits by 6 1/4
  134. 2 digits by 6.3
  135. 2 digits by 6 1/3
  136. 2 digits by 6 3/8
  137. 2 digits by 6.4
  138. 2 digits by 6 4/9
  139. 2 digits by 6 1/2
  140. 2 digits by 6 5/9
  141. 2 digits by 6.6
  142. 2 digits by 6 2/3
  143. 2 digits by 6 7/9
  144. 2 digits by 6 5/6
  145. 2 digits by 6.8
  146. 2 digits by 6 6/7
  147. 2 digits by 6 8/9
  148. 2 digits by 6.9
  149. 2 digits by 7.1
  150. 2 digits by 7 1/7
  151. 2 digits by 7.2
  152. 2 digits by 7 1/4
  153. 2 digits by 7.3
  154. 2 digits by 7 2/7
  155. 2 digits by 7.4
  156. 2 digits by 7 1/2
  157. 2 digits by 7 3/5
  158. 2 digits by 7.6
  159. 2 digits by 7.7
  160. 2 digits by 7 3/4
  161. 2 digits by 7 4/5
  162. 2 digits by 8.1
  163. 2 digits by 8 1/6
  164. 2 digits by 8.2
  165. 2 digits by 8 2/7
  166. 2 digits by 8.3
  167. 2 digits by 8 1/3
  168. 2 digits by 8 3/7
  169. 2 digits by 8 4/7
  170. 2 digits by 8 1/2
  171. 2 digits by 8.6
  172. 2 digits by 8 5/8
  173. 2 digits by 8 2/3
  174. 2 digits by 8 5/7
  175. 2 digits by 8 7/9
  176. 2 digits by 8.8
  177. 2 digits by 8 7/8
  178. 2 digits by 8 8/9
  179. 2 digits by 8.9
  180. 2 digits by 9.1
  181. 2 digits by 9.2
  182. 2 digits by 9.3
  183. 2 digits by 9 1/3
  184. 2 digits by 9.4
  185. 2 digits by 9 1/2 (four steps)
  186. 2 digits by 9 1/2 (two steps)
  187. 2 digits by 9.6
  188. 2 digits by 9 2/3
  189. 2 digits by 9 5/7
  190. 2 digits by 9.7
  191. 2 digits by 9 3/4
  192. 2 digits by 9 7/9
  193. 2 digits by 9 4/5
  194. 2 digits by 9 5/6
  195. 2 digits by 9 6/7
  196. 2 digits by 9 7/8
  197. 2 digits by 9 8/9
  198. 2 digits by 10.1
  199. 2 digits by 10.4
  200. 2 digits by 10.6
  201. 2 digits by 10.7
  202. 2 digits by 10 1/2
  203. 2 digits by 11 1/2
  204. 2 digits by 12 1/2
  205. 2 digits by 15
  206. 2,3 digits by 16 2/3
  207. 2 digits by 18
  208. 2 digits by 19 1/2
  209. 2 digits by 20 1/2
  210. 2 digits by 21
  211. 2 digits by 22
  212. 2 digits by 23
  213. 2 digits by 24
  214. 2,3 digits by 25
  215. 2 digits by 26
  216. 2 digits by 27
  217. 2 digits by 28
  218. 2 digits by 29
  219. 2 digits by 29 1/2
  220. 2 digits by 30 1/2
  221. 2 digits by 31
  222. 2 digits by 32
  223. 2 digits by 33
  224. 2 digits by 33 1/3
  225. 2 digits by 34
  226. 2 digits by 35
  227. 2 digits by 36
  228. 2 digits by 37
  229. 2 digits by 37 1/2
  230. 2 digits by 38
  231. 2 digits by 39
  232. 2 digits by 39 1/2
  233. 2 digits by 40 1/2
  234. 2 digits by 42
  235. 2 digits by 43
  236. 2 digits by 44
  237. 2 digits by 45
  238. 2 digits by 46
  239. 2 digits by 47
  240. 2 digits by 48
  241. 2 digits by 49 (a)
  242. 2 digits by 49 (b)
  243. 2 digits by 49 1/2
  244. 2 digits by 50 1/2
  245. 2 digits by 51
  246. 2 digits by 52
  247. 2 digits by 53
  248. 2 digits by 54
  249. 2 digits by 55 (a)
  250. 2 digits by 55 (b)
  251. 2 digits by 56
  252. 2 digits by 57
  253. 2 digits by 58
  254. 2 digits by 59
  255. 2 digits by 59 1/2
  256. 2 digits by 60 1/2
  257. 2 digits by 61
  258. 2 digits by 62
  259. 2 digits by 63
  260. 2 digits by 64
  261. 2 digits by 65
  262. 2 digits by 66
  263. 2 digits by 67
  264. 2 digits by 68
  265. 2 digits by 69
  266. 2 digits by 69 1/2
  267. 2 digits by 70 1/2
  268. 2 digits by 71
  269. 2 digits by 72
  270. 2 digits by 73
  271. 2 digits by 74
  272. 2,3 digits by 75
  273. 2 digits by 76
  274. 2 digits by 77
  275. 2 digits by 78
  276. 2 digits by 79
  277. 2 digits by 79 1/2
  278. 2 digits by 80 1/2
  279. 2 digits by 81
  280. 2 digits by 82
  281. 2 digits by 83
  282. 2 digits by 84
  283. 2 digits by 85
  284. 2 digits by 86
  285. 2 digits by 87
  286. 2 digits by 88
  287. 2 digits by 89
  288. 2 digits by 89 1/2
  289. 2 digits by 90 1/2
  290. 2 digits by 91
  291. 2 digits by 92
  292. 2 digits by 93
  293. 2 digits by 94
  294. 2 digits by 95
  295. 2 digits by 97
  296. 2 digits by 98
  297. 2 digits by 99
  298. 3 digits by 99
  299. 2,3 digits by 101
  300. 2 digits by 102 + 11
  301. 2 digits by 103 + 12
  302. 2 digits by 125
  303. 3 digits by 143
  304. 2 digits by 166 2/3
  305. 2 digits by 198
  306. 2 digits by 201 + 11
  307. 2 digits by 202 + 11
  308. 2 digits by 250
  309. 2 digits by 297
  310. 2 digits by 375
  311. 2 digits by 396
  312. 2 digits by 495
  313. 2 digits by 594
  314. 2 digits by 625
  315. 2 digits by 693
  316. 2 digits by 792
  317. 2 digits by 875
  318. 2 digits by 891
  319. 2 digits by 999
  320. 2,3 digits by 1001 + 21,201
  321. 2-4 digits by 1000, + 21, 201, 2001
  322. 2-5 digits by 100001
  323. 1 rep. by 9 rep.
  324. 1 rep. by 12 rep.
  325. 1 rep. by 13 rep.
  326. 1 rep. by 14 rep.
  327. 1 rep. by 15 rep.
  328. 1 rep. by 16 rep.
  329. 1 rep. by 17 rep.
  330. 1 rep. by 18 rep.
  331. 1 rep. by 19 rep.
  332. 1 rep. by 21
  333. 1 rep. by 22
  334. 1 rep. by 23
  335. 1 rep. by 24
  336. 1 rep. by 25
  337. 1 rep. by 26
  338. 1 rep. by 27
  339. 1 rep. by 29
  340. 1 rep. by 33
  341. 1 rep. by 41
  342. 1 rep. by 44
  343. 1 rep. by 45
  344. 1 rep. by 55
  345. 1 rep. by 66
  346. 1 rep. by 77
  347. 1 rep. by 88
  348. 1 rep. by 99
  349. 1 rep. by 222
  350. 1 rep. by 333
  351. 2 rep. by 5 rep.
  352. 2 rep. by 9 rep.
  353. 2 rep. by 12
  354. 2 rep. by 13
  355. 2 rep. by 14
  356. 2 rep. by 15
  357. 2 rep. by 16
  358. 2 rep. by 17
  359. 2 rep. by 22
  360. 2 rep. by 24
  361. 2 rep. by 28
  362. 2 rep. by 29
  363. 2 rep. by 33
  364. 2 rep. by 44
  365. 2 rep. by 45
  366. 2 rep. by 55
  367. 2 rep. by 66
  368. 2 rep. by 77
  369. 2 rep. by 88
  370. 2 rep. by 99
  371. 3 rep. by 6 rep.
  372. 3 rep. by 9 rep.
  373. 3 rep. by 13
  374. 3 rep. by 14
  375. 3 rep. by 15
  376. 3 rep. by 22
  377. 3 rep. by 23
  378. 3 rep. by 24
  379. 3 rep. by 35
  380. 3 rep. by 55
  381. 3 rep. by 66
  382. 3 rep. by 77
  383. 3 rep. by 88
  384. 3 rep. by 99
  385. 4 rep. by 13
  386. 4 rep. by 14
  387. 4 rep. by 15
  388. 4 rep. by 17
  389. 4 rep. by 22
  390. 4 rep. by 24
  391. 4 rep. by 28
  392. 4 rep. by 31
  393. 4 rep. by 36
  394. 4 rep. by 42
  395. 4 rep. by 44
  396. 4 rep. by 55
  397. 4 rep. by 66
  398. 4 rep. by 88
  399. 4 rep. by 99
  400. 4 rep. by 3 rep.
  401. 4 rep. by 5 rep.
  402. 4 rep. by 9 rep.
  403. 5 rep. by 15
  404. 5 rep. by 25
  405. 5 rep. by 28
  406. 5 rep. by 33
  407. 5 rep. by 55
  408. 5 rep. by 66
  409. 5 rep. by 77
  410. 5 rep. by 88
  411. 5 rep. by 99
  412. 5 rep. by 9 rep.
  413. 6 rep. by 9 rep.
  414. 6 rep. by 12
  415. 6 rep. by 15
  416. 6 rep. by 16
  417. 6 rep. by 22
  418. 6 rep. by 31
  419. 6 rep. by 32
  420. 6 rep. by 33
  421. 6 rep. by 43
  422. 6 rep. by 55
  423. 6 rep. by 66
  424. 6 rep. by 77
  425. 6 rep. by 88
  426. 6 rep. by 444
  427. 6 rep. by 888
  428. 7 rep. by 9 rep.
  429. 7 rep. by 15
  430. 7 rep. by 17
  431. 7 rep. by 32
  432. 7 rep. by 33
  433. 7 rep. by 42
  434. 7 rep. by 44
  435. 7 rep. by 55
  436. 7 rep. by 66
  437. 7 rep. by 77
  438. 7 rep. by 88
  439. 7 rep. by 99
  440. 8 rep. by 9 rep.
  441. 8 rep. by 22
  442. 8 rep. by 23
  443. 8 rep. by 24
  444. 8 rep. by 29
  445. 8 rep. by 36
  446. 8 rep. by 44
  447. 8 rep. by 55
  448. 8 rep. by 66
  449. 8 rep. by 88
  450. 9 rep. by 14
  451. 9 rep. by 22
  452. 9 rep. by 25
  453. 9 rep. by 27
  454. 9 rep. by 33
  455. 9 rep. by 44
  456. 9 rep. by 55
  457. 9 rep. by 77
  458. 9 rep. by 88
  459. 9 rep. by 99
  460. 3 repeating by 2, /37
  461. 3 repeating by 5, /37
  462. 9 rep. by 3, /12345679
  463. multi-digits by 8 + last digit
  464. by 8, add number, - 20
  465. integer + 1/2 times, + 1
  466. sum,difference of 2,1 digits
  467. two mixed numbers
  468. two mixed numbers,fractions
  469. 4 digits by 99
  470. 4 digits by 137, then 73; -1200
  471. 5 digits by 9091, then 11; -1200

 Dividing Numbers

 Adding Numbers

 Subtracting Numbers

 Finding Percents

Calculation
Practice Exercises

Full List



   Multiplying a 2-digit number by 1001
              and adding 21

  1. Select a 2-digit number.
  2. Write it twice.
  3. Write one zero between the 2-digit numbers.
  4. Add 21.

    Example:

    1. 12 × 1001 = 12012
      12012 + 21 = 12033
    2. So 12 × 1001 + 21 = 12033

   Multiplying a 3-digit number by 1001
              and adding 201

  1. Select a 3-digit number.
  2. Write it twice.
  3. Add 201.

    Example:

    1. 123 × 1001 = 123123
    2. 123123 + 201 = 123324
    3. So 123 × 1001 + 201 = 123324

Create variations by changing the number to be added or by giving a number to be subtracted. In either case, make the number an easy one to handle mentally


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31 March 1996
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