Did you notice in Table 5.1 that no rule for 7 was given? Here is a rule

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Did you notice in Table 5.1 that no rule for 7 was given? Here is a rule for determining if counting number n is divisible by 7. Any number has a units digit (it may be 0), a tens digit, a hundreds digit, and so forth. To see if n is divisible by 7, separate n into a units digit, un, and all the digits to the left of un, 10rn. Then the test for divisibility by 7 is

7 (r2u,) if and only if 7 |n For example, we see that 7 divides 616 because 61 - 2(6) = 49 and 7 divides 49.

a. 364

b. 1,283

c. 251,895

d. 627,746


Table 5.1

N is divisible by 1 23 2 4 5 6 8 O 10 12 Test all N if the last digit is divisible by 2. if the sum of the

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