The answer will depend on the divisibility rules list.
For any practical purpose, it is easier to simply divide, instead of looking for fancy divisibility rules. However, you can apply the divisibility rules for 3 and for 7. This works because (a) their product is 21, and (b) these numbers are relatively prime.
It isn't worthwhile to invent or memorize complicated divisibility rules for lots of numbers. Just carrying out the divisions is faster in most cases.
If the last 4 digits are divisible by 80, the entire number is divisible by 80.But really, it is hardly worth-while to learn divisibility rules for a large amount of numbers; only for a few small numbers. Normally it is easier to just do the division.
use divisibility rules to find at least four factors of the number 19
Its really easy all you have to do is divide without leaving a remainder
The divisibility rules for a prime number is if it is ONLY divisible by 1, and itself.
3 and 9. And they divide into 123456789 whether or not you use divisibility rules!
divided by what number use your divisibility rules
For any practical purpose, it is easier to simply divide, instead of looking for fancy divisibility rules. However, you can apply the divisibility rules for 3 and for 7. This works because (a) their product is 21, and (b) these numbers are relatively prime.
It isn't worthwhile to invent or memorize complicated divisibility rules for lots of numbers. Just carrying out the divisions is faster in most cases.
With the common divisibility rules, you can quickly see that it is divisible by 5, and by 9 (3 x 3). If you divide 225 by each of these numbers, you should be able to get the remaining factors quickly, as well.
If the last 4 digits are divisible by 80, the entire number is divisible by 80.But really, it is hardly worth-while to learn divisibility rules for a large amount of numbers; only for a few small numbers. Normally it is easier to just do the division.
I've never heard of a "friendly number strategy" per se; but there are specific rules for "divisibility" that you can use to help break up large numbers. For example, if the number is even, it is divisible by 2; if the sum of the numbers
Factors are divisors. If you know the divisibility rules, you know that 80 is divisible by 1, 2, 4, 5 and 8. If you divide 80 by those numbers, you find the other half of the factor pairs.
Divisibility rules help you find the factors of a number. Once you've found the factors for two or more numbers, you can find what they have in common. Take 231 and 321. If you know the divisibility rules, you know that they are both divisible by 3, so 3 is a common factor.
You can always check on the divisibility of a number by dividing it into another number. But if you know the divisibility rules, you can get that information easier and faster.
use divisibility rules to find at least four factors of the number 19