color(brown)("When you multiply and the signs are the same the answer is")When you multiply and the signs are the same the answer is color(brown)("positive. If they are not the same the answer is negative.")positive. If they are not the same the answer is negative.
In this case they are not the same so the answer is negative.
It is mathematically wrong to say 'the answer is a minus.'
Minus is an action. Negative is a state (condition).
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color(brown)("To avoid the decimal in the early stages of the calculation do this:")To avoid the decimal in the early stages of the calculation do this:
12.6 = 1260xx1/10012.6=1260×1100
0.81 = 81xx1/1000.81=81×1100
So we have:
1260xx81xx1/100xx1/100" "->" "1260xx81xx1/100001260×81×1100×1100 → 1260×81×110000
We leave the xx1/10000×110000 until the end
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Split 81 into 80+180+1
color(blue)("The actual calculation")The actual calculation
" "80xx1260 rarr 100800 80×1260→100800
" "1xx1260 ->ul(color(white)(..) 1260) larr" add"
" "color(white)(.)102060
102060xx1/10000 = 10.206larr" now we adjust the value"
color(blue)("But the answer is negative "-10.206
