(ds): if the opertation *is one of the four arithmetic operations addition, subtraction, mulitiplication, and division,is (6*2)*4=6*(2*4) 1.3*2>3 2.3*1>3 答案是A
(ps):when a certain tree was first planted, it was 4 feet tall, and the height of the tree increased by a cnstant amount each year for the next 6 year. at the end of the 6th year, the tree was 1/5 taller than the end of the 4th year. by how many feet did the height of the tree increased each year. 3/10 2/5 1/2 2/3 6/5 答案是2/3