Question 176672
Estimate by rounding up measurements to the nearest whole number. 
Remember if you round down you may not have enough carpet.
10 1/2 = 11
9 3/4 = 10
19 1/4 = 20
18 1/2 = 19
{{{A[1]=11*10=110}}}
{{{A[2]=20*19=380}}}
{{{A[t]=A[1]+A[2]=110+380=490}}}
You need about 490 square feet of carpet.
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We can get the exact amount needed. 
Change the measurements to pure fractions first.
{{{10+1/2=20/2+1/2=21/2}}}
{{{9+3/4=36/4+3/4=39/4}}}
{{{19+1/4=76/4+1/4=77/4}}}
{{{18+1/2=36/2+1/2=37/2}}}
Now you can calculate the square footage of each room.
{{{A[1]=(21/2)*(39/4)=819/8}}}
{{{A[2]=(77/4)*(37/2)=2849/8}}}
The total area is the sum of the two rooms,
{{{A[t]=A[1]+A[2]=819/8+2849/8=3668/8=917/2=458.5}}}
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You estimated 490 sq.ft. while the exact fit is 458.5 sq. ft.. 
That's a good estimate. 
Rule of thumb is to always order 10% more.