Mental Arithmetic
Quantity— Unit— Number
Lesson 1
1. Make a mental picture of a line 12 in. long and also of a unit of measure 3 in. long. How many times will the 3-in. unit measure the quantity 12 in.?
2. The number 4 obtained in example 1 is 4 what? 4 units of 3-in. in what?
3. This number 4 is often called the ratio of 12in. to 3 in. What is the ratio of 12 in. to 4 in. ?
4. What part of 12 in. is equal to 3 in.? 1 is often called the ratio of 3 in. to 12 in. What is the ratio of 4 in. to 12 in. ?
5. Find the number of 3—in. units of length in each of these quantities : 15 in. ; 2 ft. ; 30 in.; 1 yd.; 1 ft. 6 in. ; 2 ft. 3 in. What is the ratio of each of these quantities to the unit? of the unit to each quantity ?
6. In question 5 how did you find the number of 3-in. units in each quantity ?