Exercise 35
1. Which of the following are prime numbers?
17, 29, 25, 33, 19, 6
Please Solve it
Answers
Answer:
here's your answer hope it helps
Step-by-step explanation:
Work on the easy ones first. Any even number is divisible by 2, so 12 is gone.
A trick for 3′s: add the numbers together and see if the result is divisible by 3. If the result is multiple digits, keep adding until they are 1 digit.
15: 1+5=6. 6 is divisible by 3. Not a prime
17: 1+7=8. Not divisible by 3. Possible prime.
21: 2+1=3. 3 is divisible by 3. Not a prime.
27: 2+7=9. 9 is divisible by 3. Not a prime.
—This works for huge numbers too. 24561: 2+4+5+6+1=18 1+8=9. 9 is divisible by 3, so 24561 is divisible by 3. Cool, huh?
This boils your question down to whether or not 17 is prime.
It's not divisible by 2 or 3. That means it's also not divisible by multiplies of those, so we can also mark off 4, 6 and 8.
We don't have to worry about anything higher than 8 because we would be dealing with fractions and not whole numbers.
That leaves us with 5 and 7. Will either 5 or 7 evenly go into 17? No. So 17 is prime.
(Yes there are quicker ways, but my intention is to create a pattern that is easy to understand and follow)