Lesson7
VERTICALLY AND CROSSWISE MULTIPLICATION
Consider the conventional multiplication of two 2 digit numbers 12 and 23
shown below:
12
X 23
36
24x
276
This is normally called long multiplication but
actually the answer can be written straight down
using the VERTICALLY AND CROSSWISE
formula.
There are 3 steps:
a) Multiply vertically on the left: 2 x 3= 6
This gives the first figure of the answer.
b) Multiply crosswise and add: 1 x 3 + 2 x 2 = 7
This gives the middle figure.
c) Multiply vertically on the right: 1 x 2 = 3
This gives the last figure of the
l 21 x 26 = 546
The method is the same as above
except that we get a 2-figure number, 14, in the
middle step, so the 1 is carried over to the left
(4 becomes 5).
l 33 x 44 = 1452
There may be more than one carry in a sum:
Vertically on the left we get 12.
Crosswise gives us 24, so we carry 2 to the left
and mentally get 144.
Then vertically on the right we get 12 and the 1
here is carried over to the 144 to make 1452.
This is multiplication of 2 digits numbers .Now we learn 3 digits multiplication
3 Digits Multiplication
Let us try to understand this by an example.
123 x321=????
Step 1 We start from right and multiply last digits of both numbers vertically
3x1 =3
Step 2 Multiply last two digits crosswise and add together and write before step one figure
2x1+3x2=2 + 6 = 8
Step 3 Multiply first and last digits crosswise and middle digit vertically and add together and write total before
step 2 figure
1x1 +3x3 +2x2 =1+9+3=14
Step 4 Multiply first two digits crosswise and add together and write before step 3 figure also add carry
2x1 +3x2+1 =9
Step 5 Multiply first digits of both numbers vertically and write before step 4 figure
1 2 3
I
3 2 1
3 9 14 8 3 1x3=3
Our required answer is 39483
Practice Test
28 x89 28x62 56x48 236 x456 58x 78
259x 789 289 x89 * 87 x56 211 x879 25x89
Hint 289 x089
289
x 089
0x2 / 2x8+8x0=16 / 2x9+8x8+0x9=82 / 8x9+8x9=144 / 9x9=81
16+9=25 / 82+15=97 /144+8 =152 /81
= 25721
Back Home Next
0 comments:
Post a Comment