« 6th grade h.w. | Main | 7th grade HW »

We have been working on a bobsled method to find the prime factors of a number. Bobsled is a reverse division where you divide only by prime numbers. I tell the students to always write the first 7 or 8 prime numbers on top of their papers for a reminder...they all know them (2,3,5,7,11,13,17,19,23..). Today we began doing double bobsleds where we find the prime factors of two numbers and then find the prime factors that they share. For ex. if we wanted to find the GCF (greatest common factor) of 27 and 45. We first divide 27 by it's prime factors and get 3x3x3. When we divide 45 by it's prime factors (bobsled) we get 3x3x5. * you stop dividing when the last number is prime. Next we look for the 'common' numbers or pairs. There are 2 pairs of 3 so we write 3x3 and multiply. The answer is 9. 9 is the largest factor that can go into both 27 and 45 evenly. GCF=9 Sometimes you get numbers like 14 and 33. Their GCF is 1 because they share no other common factors. Tomorrow we will be learning to triple bobsled. The idea is basically the same but all three numbers will have to share a common factor! So far our class is really showing they understand this concept!

Posted by Mrs. Jennings