DIVISIBILITY These tests for divisibility will prove useful in reducing fractions, in cancellation, and elsewhere in arithmetic. 1. All even numbers are divisible by 2. 2. If the sum of the figures of a number is divisible by 3, the number is divisible by 3. 258 is divisible by 3, because the sum of 2 and 5 and 8- that is, 15—is divisible by 3. 3. If the last two figures of a number are zeros, or if they form a number which is divisible by 4, the given number is divisible by 4. 136 is divisible by 4, because 36 is divisible by 4. 4. Any number ending in 0 or 5 is divisible by 5. 5. Any number ending in 0 is divisible by 10. ORAL EXERCISES Tell whether these numbers are divisible by 2, 3, 4, 5, 10. What does the denominator of a common fraction show? What does the numerator show? What is a proper fraction? an improper fraction? a mixed number? Give examples of each. How is a fraction affected if the numerator is multiplied by a given number? if the numerator is divided by a given number? if the denominator is multiplied by a given number? if it is divided by a given number? |