Janice is dividing 1.92 divided by 6. Why does she exchange the place value blocks shown for 18 tenths and 12 ones ?
2 answers:
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Factor 16 and see the - factor pairs and add them, see which add to -12
-1-16=-17 nope
-2-8=-10 nope
-4-4=-8
hmm
we will solve with math
xy=16
x+y=-12
minus x both sides
y=-12-x
sub for y in other equation
x(-12-x)=16
-12x-x^2=16
add 12x+x^2 both sides
0=x^2+12x+16
use quadratic formula
if you have
ax^2+bx+c=0
x=
0=x^2+12x+16
a=1
b=12
c=16
x=
x=
x=
x=
x=
x=
or 
aprox
x=-1.52786 or -10.4721
those are the numbers
the numbes are -1.52786 or -10.4721
-1-16=-17 nope
-2-8=-10 nope
-4-4=-8
hmm
we will solve with math
xy=16
x+y=-12
minus x both sides
y=-12-x
sub for y in other equation
x(-12-x)=16
-12x-x^2=16
add 12x+x^2 both sides
0=x^2+12x+16
use quadratic formula
if you have
ax^2+bx+c=0
x=
0=x^2+12x+16
a=1
b=12
c=16
x=
x=
x=
x=
x=
x=
aprox
x=-1.52786 or -10.4721
those are the numbers
the numbes are -1.52786 or -10.4721