X decimals by Powers of 10
6.83 x 103
=6.83 x 1000 = 6,830
estimate this product: 99.2 x 82
100 x 80 = 8,000 or 100 x 82 = 8,200 (these are compatible numbers, numbers that multiply nicely with each other)
find the product: 3.5 x 0.4
1.4
open your textbook to page 140. Please answer question 22
3 x 0.8 = 2.4
2.786 x 10
27.86
estimate the product: 0.87 x 112
0.9 x 100 = 90
0.87 rounds to 0.9
112 estimates to 100, a compatible number/ easy to multiply/ estimate
When multiplying by decimal numbers, should you
1. line up the decimal point while doing your calculations
OR
2. multiply the numbers as if there were no decimal points, line up numbers on the right side (add the decimal point after you multiply the #s)
2. BE careful! when you add / subtract decimal numbers, you need to line up the decimal points to add and subtract similar place values, but when you multiply, simply right justify them and multiply. then add the decimal point the number of places to the left as the total decimal places in your factors.
Anita needs 5 pounds of bananas to make banana bread for a bake sale. Each pound of bananas costs $ 0.50. How can Anita use place-value blocks to find the total cost of the bananas? what is the total cost?
$2.50; if you use a 100 box grid, you could shade in 5 sets of 50 hundredths. this would fill two full grids and 1 half grid.
You could also think of a box, and just shade half of it to represent $0.50. Then, combine 5 of these half boxes to make a total of 2.5 or $2.50.
What should you do to the decimal point when multiplying by a power of 10?
move it to the right the number of places as multiple of 10 (ex: if you multiply by 100, move the decimal place 2 to the right; 7.35 x 100 = 735)
Joseph buys a pair of shorts for $17.95 and 4 t-shirts for $12.50 each. About how much money does he spend?
about $70
t-shirts: 13 x 4 = 52
+ shorts + 18 = $70
find the product: 0.8 x 8.6
6.88
Explain how you could break apart a 100 grid to model one tenth.
a column of 10 boxes would make on tenth. There would be 10 of such columns in a 100 grid.
open textbook to page 132, answer question #19
A = 0.8
B = 1.1
C = 0.25
D = 0.4
Use number sense to determine where the decimal belongs: 6.99 x 21 = 14679
146.79
find the product: 6.8 x 7.2
48.96
Shade 4 rows to model 0.4, shade 5 columns to model 0.5. 0.4 x 0.5 = 0.20. the rectangle created by the overlap of these rows and columns is the area of the garden containing bell peppers
turn to page 132 in textbook, answer question 23
85.5 inches
95 - 9.5
Quincey says that 3 is a good estimate for 3.4 x 0.09. Is he correct? Why?
no! if I estimate 0.09 to 0.1, that would move the decimal point one to the left...0.34 would be a closer estimate.
find the product: 9.3 x 4.1
38.13
open your textbook to page 161, answer the solve & share problem. Please be sure to write an equation.
$18.41
c=(1.2 x $3.40) + (1.5 x $2.90) + (2 x $4.99)
=4.80 + 4.35 + 9.98
=$18.41