Addition & Subtraction Problem Questions

Taking away is easier if you count up instead of down. For forty-three take twenty-seven, start at twenty-seven and hop to the next ten, which is thirty — that is three. Then hop in tens to forty, which is ten more. Then three more to forty-three. Add up all the hops: three and ten and three makes sixteen. So forty-three take twenty-seven is sixteen. Hop to the next ten first, then in tens, then the last bit.

To add a number that is near a hundred, split it into easy pieces. A hundred and nine is a hundred and nine ones. Sixty-eight plus a hundred is a hundred and sixty-eight, and nine more is a hundred and seventy-seven. Splitting the harder number works for any addition. And check the size of your answer at the end: sixty-eight and a hundred and nine are both small numbers, so something near a hundred and seventy-seven looks right.

Adding and taking away undo each other. Two parts sit inside one whole, and that one picture gives you three number sentences: twenty-seven and sixteen make forty-three, forty-three take twenty-seven is sixteen, and forty-three take sixteen is twenty-seven. They all say the same thing. So to check a take-away, add your answer back on — sixteen plus twenty-seven should give you forty-three. And to find a missing part, take the part you know away from the whole.

Change questions are two steps. First add up what was spent: two dollars eighty plus two dollars five is four dollars eighty-five. Then take that from the note: ten dollars take four eighty-five. Hop up — four eighty-five to five dollars is fifteen cents, and five dollars to ten dollars is five dollars, so the change is five dollars fifteen. Check by adding back: four eighty-five and five fifteen make ten dollars. And watch out, because four dollars eighty-five is the total spent, not the change, and the test always offers it as an answer.

Four moves cover this strand. To take away, count up to the next ten and then in tens. To add a big number, split it. To find a missing part, take the part you know from the whole. And for change, add up the spending and then take it from the note. Every one of them can be checked by adding back, and if you have a spare moment in the test, that is the check to do. Quiz and exercises now.