Answer: A
Explanation:
Ok, some that we always try to do in math is to look for "nice" numbers.
The nice numbers are numbers that are easy to work with.
Examples of these are numbers like 10, 100, etc.
suppose the next example:
9 + 3 + 1 + 7
That may seem a long addition, but we can rearange the numbers in such a way to get:
(9 + 1) + ( 3 + 7) = 10 + 10 = 20
This is specially useful when doing mental calculus.
In the given options, we have:
A) 30 + (-12) + 70
Doing it straightforward, we must:
Subtract 12 from 30, which will give us a not nice number.
30 - 12 = 18
And now add 70 to that:
18 + 70 = 88.
Now, we could use the commutative properety and get:
30 + (-12) + 70 = 30 + 70 + (-12)
in this way, in the first addition we get to 100, and then we subtract 12 units.
(30 + 70) + (-12) = 100 - 12 = 88.
Then the correct option is A.