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The Power of Ten

As 5+4=9, so 50+40=90, 500+400=900, and 5,000+4,000=9,000

10*10=100 10*100=1000 10*1000=10,000

Groups of ten shows the extent to which we use multiples of 10


Multiples of Ten in Adding and Subtracting

A sum does not change when the same number is added or subtracted, or if added then subtracted from the other

18+7=25=18+7+2-2=25 

(18+2)+(7-2)=20+5=25

Subtraction undoes the effect of addition

Rounding up to a multiple of 10

256+98+2=256+100-2=354

Subtraction is the inverse of addition

Rounding down to a multiple of 10

52-3=52-2-1=50-1=49

61-3=61-1-2=60-2=58

93-4=93-3-1=90-1=89

Multiply by the power of ten and add

42*8

42×8=40×8+2×8=320+16=336

Multiply by ten, then by ones, and add the products.

16*5=10*5+6*5=50+30=80

8*46=320+48=368








What is Division

Dividend ÷ Divisor = Quotient

The object of division is to find how many times a number, the divisor, is contained in another number, the dividend.

The answer is called the quotient.

To find how many times the divisor will equal the dividend, find how many times to subtract the divisor from the dividend.

Division and the Power of Ten

Show Dividend/Divisor as equaling the Quotient

16/8=2

280/7=is what number?

7 goes into 28 four (4) times, 7 goes into 280 forty (40) times.

280/7=40.

Quotient times the Divisor equals the Dividend

40 times 7 is 280 or 7*40=7*4*10=280

How do we divide by decomposing the dividend? 

Break up the dividend into obvious multiples of the divisor. Then divide each multiple, and add or subtract those partial quotients

265 is made up of how many 5's?

Go from what we know to what we do not know. Which number divisible by 5 is closest to the first two digits of 265? It is 25. Since 25 is divisible by 5, so is 250. Decompose 265 as 250 + 15.

Then, 265/5=250/5+15/5=50+3=53.

265 is made up of Fifty 5's + Three 5's: Fifty-three 5's.