Posted by Gabby ( 5 grade) on .
how would you test to see whether 7 is a factor of 291?

math 
Reiny,
I would divide it out and see.
or
write down the number without the last digit
29
subtract twice the digit you skipped
29
2

27
is 27 divisilbe by 7 ?
no ? , then neither was 291
for large numbers checking for divisibility by 7,
repeat the above process until you can tell.
Not very practical, but it works !!! 
math 
Gabby ( 5 grade),
why 2 if the end digit is 1?

math 
Reiny,
notice I said, "twice" the number skipped.
2x1 = 2 
math 
Gabby ( 5 grade),
i don't get it i want ms sue to help me!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

math 
Ms. Sue,
<g>
Reiny is a REAL math teacher; I'm not.
I'd just divide 291 by 7. 
math 
Gabby ( 5 grade),
WOW I BELIEVED IN YOU:P