addition 加法
how do you say 2+2=4,or 712+145=857?
in small additions,we usually say and for+,and is or are for =.
  two and two are four.
  six and five is eleven.
  what's eight and six?
in large additions,(and in more formal dtyle)we use plus for +,
and equals or is for=.
  seven hundred and tweleve plus a hundred and forty-five is/equals eight hundred and fifty-seven.

how do you say 7-4=3,or 619-428=191.?
in conversational style,dealing with small numbers,people say four from seven/is three,or seven take away four leaves/is
three.in a more formal style,or dealing with a large numbers,minus and equals are used.
six hundred and nineteen minus four hundred and twenty-eight equals a hundred and ninety-one.

how do you say 3x4=12,or 17x381=6577?
in small calculations ,the most common arrroch is to say three fours,six seven,etc,and to use are four=.
   three fours are twelve.
   six sevens are forty-two.
in large calculations,three are several possibilities.one way is to say times for x , and is or makes for=.
  sevens times three hundred and eighty-one is/makes six thousand,four hundred and seventy-seven.
in a more formal style,,we say multiplied by and equals.
  17 multiplied by 381 equals 6477

how do you say 9/3=3 or 261/9=29?
the simplest way is to use divided by and equals.
  two hundred and sixty-one divided by nine equals twenty-nine.
but in small calculations,people might say,for example, three into nine goes three
(引于牛津英语用法)