1 . doing a sum
Life is painting a picture , not doing a sum ., 生活是绘画 , 不是做算术. -- 喜欢这条.
2 . do sums
Hi , kids , let ' s do sums . OK ?, 嗨 , 孩子们 , 我们做算术吧 , 好吗?
3 . some arithmetic
he occupied himself with solving some arithmetic problems .他忙着做算术题。
4 . boing a sum
life is painting a picture , not boing a sum .生活是绘画,不是做算术。