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Mental Math Day 1. Basic Addition. Add and subtract the summands to make this easier! 1242 + 998 = ? + 1000 = 1240 + 1000 = 2240. More Basic Addition. 5346 + 445 = ? + 450 = 5341 + 450 = 5741+50 = 5791. -. +. SUMMAND 1. SUMMAND 2. You try it! (all techniques). - PowerPoint PPT Presentation
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Mental Math Day 1
Basic Addition
• Add and subtract the summands to make this easier!
1242 + 998 =
? + 1000 =
1240 + 1000 =
2240
More Basic Addition
5346 + 445 =
? + 450 =
5341 + 450 =
5741+50 =
5791
+-
SUMMAND 1 SUMMAND 2
You try it! (all techniques)
• 87654321+12345678=
• 123456789+987654321=• 1+2+3+4+5+6+7+8+9
=(1+9)+(8+2)+(7+3)+(6+4)+5
=10+10+10+10+5=45
• 2+4+6+8+10+12+14+16+18=
99999999
1111111110
2x45=90
Sum all entries - Which is More?1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100
X 1 2 3 4 5 6 7 8 9 10
1 1 2 3 4 5 6 7 8 9 10
2 2 4 6 8 10 12 14 16 18 20
3 3 6 9 12 15 18 21 24 27 30
4 4 8 12 16 20 24 28 32 36 40
5 5 10 15 20 25 30 35 40 45 50
6 6 12 18 24 30 36 42 48 54 60
7 7 14 21 28 35 42 49 56 63 70
8 8 16 24 32 40 48 56 64 72 80
9 9 18 27 36 45 54 63 72 81 90
10 10 20 30 40 50 60 70 80 90 100
SUM All ENTRIES1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100
Total is 10x55+100x45
1 2 3 4 5 6 7 8 9 10 SUM= 55
11 12 13 14 15 16 17 18 19 20 55+100
21 22 23 24 25 26 27 28 29 30 55+200
31 32 33 34 35 36 37 38 39 40 55+300
41 42 43 44 45 46 47 48 49 50 55+400
51 52 53 54 55 56 57 58 59 60 55+500
61 62 63 64 65 66 67 68 69 70 55+600
71 72 73 74 75 76 77 78 79 80 55+700
81 82 83 84 85 86 87 88 89 90 55+800
91 92 93 94 95 96 97 98 99 100 55+900
Total is 10x55+100x45=550+4500=5000+50
=50501 2 3 4 5 6 7 8 9 10 SUM= 55
11 12 13 14 15 16 17 18 19 20 55+100
21 22 23 24 25 26 27 28 29 30 55+200
31 32 33 34 35 36 37 38 39 40 55+300
41 42 43 44 45 46 47 48 49 50 55+400
51 52 53 54 55 56 57 58 59 60 55+500
61 62 63 64 65 66 67 68 69 70 55+600
71 72 73 74 75 76 77 78 79 80 55+700
81 82 83 84 85 86 87 88 89 90 55+800
91 92 93 94 95 96 97 98 99 100 55+900
X 1 2 3 4 5 6 7 8 9 10
1 1 2 3 4 5 6 7 8 9 10
2 2 4 6 8 10 12 14 16 18 20
3 3 6 9 12 15 18 21 24 27 30
4 4 8 12 16 20 24 28 32 36 40
5 5 10 15 20 25 30 35 40 45 50
6 6 12 18 24 30 36 42 48 54 60
7 7 14 21 28 35 42 49 56 63 70
8 8 16 24 32 40 48 56 64 72 80
9 9 18 27 36 45 54 63 72 81 90
10 10 20 30 40 50 60 70 80 90 100
Add up all the numbers in this table (in your head!)
X 1 2 3 4 5 6 7 8 9 10 SUM=55
1 1 2 3 4 5 6 7 8 9 10 55
2 2 4 6 8 10 12 14 16 18 20 2x55
3 3 6 9 12 15 18 21 24 27 30 3x55
4 4 8 12 16 20 24 28 32 36 40 4x55
5 5 10 15 20 25 30 35 40 45 50 5x55
6 6 12 18 24 30 36 42 48 54 60 6x55
7 7 14 21 28 35 42 49 56 63 70 7x55
8 8 16 24 32 40 48 56 64 72 80 8x55
9 9 18 27 36 45 54 63 72 81 90 9x55
10 10 20 30 40 50 60 70 80 90 100 10x55
Sum is 55x55 + 55+55=?
55 more
Sum is 55x55 + 2x55=?
=(50+5)x(50+5)+2x55
=(50x50)+5x50+50x5+5x5+2x55
So we need the total of• 2500• 250• 250• 25• 110
Sum is 55x55 + 55=?
So we need the total of• 2500• 250• 250• 25• 110
This is 2500+500+135=3135
