Be Careful!! Don’t just replace the “chopped off” numbers with zeroes! When you round, you are really reducing the number of digits behind the decimal!
Here are some numbers to round to the nearest hundredth.
1.3247 1.32
0.987 0.99
4.89721 4.90
Because we are rounding to the nearest hundredth, each of the numbers ends up with two digits behind the decimal. What if we had been rounding to the nearest tenth? (answer: Rounding to the nearest tenth leaves one decimal place. In the example: 1.3, 1.0, 4.9)
When you add decimals, line the decimals up – one on top of the other.
You have to add the tenths to the tenths, the hundredths to the hundredths, and so on – just as when you add whole numbers, you add ones to ones and tens to tens.
In the second equation, both 42 and 6 have been multiplied by ten. Because both numbers were multiplied by the same thing, the quotient did not change.
We can use that trick to divide numbers with decimals.
Because moving the decimal to the right is just like multiplying by ten, if we move the decimal the same number of places in both numbers, our quotient stays the same.
If these were whole numbers, you would say, “How many times will 12 go into 13?” But it’s harder to think of .12 and .13. If you could move the decimal of the divisor (.12) over 2 places, you would have a whole number. You can do that as long as you move the decimal of the dividend over 2 places as well.
NOTICE: The decimal moved straight up from the dividend to the quotient. Lining up the number in the quotient and the dividend is VERY important because if they are wrong, your decimal will be in the wrong place. 12. 13.2 1.1 -12 1 2 -1 2 0
First of all, let’s estimate how many .4’s it would take to make 1.25 .4 + .4 + .4 = 1.2 so it will take 3 groups of .4 plus a little more to make 1.25 .4 1.25
35.
Dividing Decimals First, move the decimal in the divisor and the dividend. In this case, we have pulled down all our numbers, but we still have a remainder. DO NOT tack your remainder onto the end of your answer! 4. 12.5 3.1 -12 05 -4 1
Remember that adding zeroes at the end of a number does not change its value.
12.5 = 12.50000
If you need to keep dividing, just annex zeroes, pull down & keep dividing until you get a remainder of zero (or until you see a pattern.)
37.
Annexing Zeroes- -8 20 -20 0 When you get a remainder of zero, you can stop pulling down zeroes. 4. 12.5 000 3.125 -12 05 -4 10
38.
Check Your Work! The original problem was 1.25 ÷ .4. The quotient was 3.125 Check: 3.125 x .4 1.2500 3 digits 1 digit 4 digits Since 1.2500 = 1.25, our answer is correct.
First, move the decimal. . Put the decimal on the quotient line. .3 5.56 3. 55.6
42.
Repeating Decimals When you’ve pulled down all your numbers and you still have a remainder, you need to annex zeroes and keep going. 3. 55.6 18.5 -3 25 -24 16 -15 1
43.
Repeating Decimals -9 10 From here on, no matter how many zeroes we pull down, we will always get 10 and the next number will always be 3. The 3 is repeating. 3. 55.6 000 18.533 -3 25 -24 16 -15 10
Be the first to comment