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Mult. 11
Addition by rounding
Squaring numbers ending in 5/close to 50
Mult. 101/mult. one’s digits add to ten
Mult. by 25.75/125
100

9 x 11

99

100

13 + 31 + 61

105

100

25 x 25

625

100

53 x 101

5353

100

43 x 25

1075

200

23 x 11

253

200

1+2+3+......+15

120

200

85 x 85

7225

200

47 x 43

2021

200

87 x 75

6525

300

47 x 11

517

300

1+2+3+.....+30

465

300

51 x 51

2601

300

38x32 + 88 x 101

10104

300

173 x 125

21625

400

123 x 11

1353

400

331 + 709 + 441 + 303

1784

400

125 x 125 + 53 x 53

18434

400

128 x 101 + 89 x 81

20137

400

27 x 75 + 41 x 125 + 36 x 25

8050

500

357 x 11

3927

500

1+2+3+.......+100

5050

500

505 x 505 + 47 x 47

257234

500

101 x 201 + 98 x 92

29317

500

173 x 25 + 125 x 125 + 75 x 160

31950