How_To_Be_Good_At_Math

CALCULATING • THE LATTICE METHOD 127

We can use the lattice method to multiply decimals,

too. We just need to find where the decimal points meet.

The carried

1 ten goes here

Read the answer

from the top left

to the bottom right

Write the

total of the

diagonal at

the edge

Keep adding the numbers across each

diagonal, until we reach the top left

corner. We are left with the numbers

4, 9, 9, and 2. So, the answer is 4992.

Starting from the bottom right corner,

add the numbers along each diagonal.

The first diagonal has just the number 2, so

we write 2 at the edge end of the diagonal.

Now add the numbers in the second

diagonal: 8 + 3 + 8 = 19. Write 9 at the

end of the diagonal and carry the 1 ten into

the next diagonal to add on at the next stage.

Let’s multiply 3.59 by 2.8. First, write the

two numbers along the edges of the

lattice, including the decimal points. Work

through the steps in the same way that we

did with the whole numbers above.

Next, look down from the decimal point

at the top and along from the decimal

point at the side and find where they meet

inside the lattice.

Follow the diagonal

line from this point

down to the bottom of

the lattice and write the

decimal point between the

two numbers at the end.

So, 3.59 × 2.8 = 10.052

6

4

(^78) ×
4
2 3
4
2
2
8 2
8
6
4
(^78) ×
4
2 3
4
9 2
2
8 2
8
1
6
4
(^78) ×
4
2 3
4
4
9
9 2
2
8 2
8
1
2
8
5 9
.
.
.
×
0 1
3
42 7
1
0
1
0 5 2
6 0
2
8
1
Find where the
decimal points meet
Write the decimal
point here
04
.
Multiplying decimals using the lattice method
78 × 64 = 4992
So, 78 × 64 = 4992
1
1
126-127_The_lattice_method.indd 127 29/02/2016 16:39