The answer is 0, 1/3 of 21 is 7, 7-1=6, 1/2 of 12= 6, and 6-6=0. Hope this helps!
Answer:
Roughly 18,000
Step-by-step explanation:
When you need to do rough mental math, you can do something like 720 vs 25 or 30 which is pretty simple to do in your head.
If you are very proficient in mental math, you can do something like 720 * 25, which is harder, but if you know the tricks, you can do this quickly.
720 * 25
Multiply 25 by 7.
175
Add two zeros.
17,500
Multiply 25 by 2
50
Add a zero.
500.
17500 + 500 = 18000
Xy is the number
A) x + y = 7
B) 10y + x = 10x + y + 9
collecting terms of equation B
B) -9x + 9y = 9
multiplying A) by 9
A) 9x + 9y = 63 then adding it to equation B)
B) -9x + 9y = 9
18y = 72
y = 4
x = 3
The number is 34
Answer:

Step-by-step explanation:

Factor the equation:


Rewrite to suit the format of multiplying two fractions. Remember, dividing two fractions is the same as multiplying the first fraction by the reciprocal of the second. A reciprocal of a fraction is when one switches the place of the numerator and the denominator, that is, the value on top (numerator), and the value on the bottom (denominator).

Simplify, take out common terms that are found on both the numerator and denominator


Consider expression 
1. Use property

Then

2. Use property

Then

3. Use property

Then

4. Use property

Then

Answer: correct option is B.