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Q: How will you test to see whether 7 is a factor or 291?

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Divide 7 into 291. If the answer is an integer, 7 is a factor.

Divide it. It isn't.

7 doesn't have an easy test. But when I see that 291 is made up of 280 + 11, I know that 7 is not a factor.

There isn't an easy test for 7. You have to divide it. 7 is not a factor of 291.

Divide 7 into 291. If it comes out evenly, it's a factor. It doesn't, so it's not.

Divide 291 by 7 and see if you get a whole number or is there a remainder. If it is not a whole number, then it is not a factor. 7 goes into 291 41 times with a remainder of 4, so it is not a factor.

No. If you divide 291 by 12 you will see that it does not go in 291 an exact number of times.

Divide your number by 7 and see if there is a remainder. If there is a remainder, 7 is not a factor.

Divide 7 into 29. If the answer is an integer with no remainder, it's a factor.

There is no trick to find out easily if 7 is a factor of a given number, like 291. There are easy rules for finding out if 3 is a factor of a given number (adding up the digits, again and again until you have a single digit and then see if the single digit is a multiple of 3 or not: 291 includes digits 2, 9, 1 2 + 9 + 1 = 12 1 + 2 = 3 3 is a multiple of 3, so 291 is a multiple of 3. Indeed 291 = 3 x 97).For 7, the only was is to work out the division directly and see if there is any remainder or not: 291 / 7 = 41 remainder 4 thus 291 is not a multiple of 7, which is the same as saying that 7 is not a factor of 291.----------Actually there is a way to find whether a number has a factor of 7. It is discussed in Arthur Benjamin's "Secrets of Mental Math" Book, mental division, page 100. It states:Add or substract multiples of 7 to leave the last digit position as zero, then eliminate and continue until nothing is left.Example with 52925292 ends in 2, 6X7 42, substract 425292 -42 5250, eliminate the zero525, ends in 5 7x5 35, substract525-35490, eliminate the zero.49, which we know is a multiple of 7 (7^2). > 5292 is a multiple of 7.Another example16184, ends in 4, substract 1416170>1617 ends in 7, you can also add up to zero. Add 631680 >168, ends in 8, substract 28140> 14 which is divisible by 7. This number has a factor of 7.291 , last digit is one, 3x7 21, substract.291 - 21 250 > 25 which is not a multiple of 7. > 291 does not have a factor of 7.

It's easy to see whether 2 is a factor of a number because 2 is a factor of every even number and not a factor of any odd number.

The ISBN of As I See It is 978-81-291-1876-9.

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