1. The boys and girls of the Welfare Club plan to earn money to buy a victrola. There are 23 boys and girls. They can get a good second-hand victrola for $5.75. How much must each earn if they divide the cost equally?
Here is the best way to find out:
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$.25 23|$5.75 46 115 115 |
Think how many 23s there are in 57. 2 is right. Write 2 over the 7 of 57. Multiply 23 by 2. Write 46 under 57 and subtract. Write the 5 of 575 after the 11. Think how many 23s there are in 115. 5 is right. Write 5 over the 5 of 575. Multiply 23 by 5. Write the 115 under the 115 that is there and subtract. There is no remainder. Put $ and the decimal point where they belong. Each child must earn 25 cents. This is right, for $.25 multiplied by 23 = $5.75. |
2. Divide $71.76 equally among 23 persons. How much is each person's share?
3. Check your result for No. 2 by multiplying the quotient by the divisor.
Find the quotients. Check each quotient by multiplying it by the divisor.
| 4. 23 | $99.13 | 5. 25 | $18.50 | 6. 21 | $129.15 | 7. 13 | $29.25 | 8. 32 | $73.92 |
1 bushel = 32 qt.
9. How many bushels are there in 288 qt.? 10. In 192 qt.? 11. In 416 qt.?
Crucial experiments are lacking, but there are several lines of well-attested evidence. First of all, there can be no doubt that the great majority of pupils learn these manipulations at the start from the placing of units under units, tens under tens, etc., in adding, to the placing of the decimal point in division with decimals, by imitation and blind following of specific instructions, and that a very large proportion of the pupils do not to the end, that is to the fifth school-year, understand them as necessary deductions from decimal notation. It also seems probable that this proportion would not be much reduced no matter how ingeniously and carefully the deductions were explained by textbooks and teachers. Evidence of this fact will appear abundantly to any one who will observe schoolroom life. It also appears in the fact that after the properties of the decimal notation have been thus used again and again; e.g., for deducing 'carrying' in addition, 'borrowing' in subtraction, 'carrying' in multiplication, the value of the digits in the partial product, the value of each remainder in short division, the value of the quotient figures in division, the addition, subtraction, multiplication, and division of United States money, and the placing of the decimal point in multiplication, no competent teacher dares to rely upon the pupil, even though he now has four or more years' experience with decimal notation, to deduce the placing of the decimal point in division with decimals. It may be an illusion, but one seems to sense in the better textbooks a recognition of the futility of the attempt to secure deductive derivations of those manipulations. I refer to the brevity of the explanations and their insertion in such a form that they will influence the pupils' thinking as little as possible. At any rate the fact is sure that most pupils do not learn the manipulations by deductive reasoning, or understand them as necessary consequences of abstract principles.