Lecture from Wednesday, September 28.

1. Agenda 9/28/11 1. Divisibility Rules 2. Review HW (Word Problems) 3. Choosing the Operation 4. Multistep Problems HW: Exercises 3 and 6

2. Divisibility Rules Review: A number is evenly divisible by three if the sum of the digits is evenly divisible by three. 678 4,869,478 674,289 Yes! No! Yes!

3. Divisibility Rules Review: A number is evenly divisible by four if the two rightmost digits are evenly divisible by four. 7,594,875,934 9,376,520 45,336 No! Yes! Yes!

4. Five A number is evenly divisible by five if the rightmost digit is a 5 or a 0. Example 74,836,340 is evenly divisible by five because the rightmost digit is zero.

5. Six A number is evenly divisible by six if it is divisible by both two and three. Example 222 is divisible by six because it is even and 2 + 2 + 2= 6, which makes it divisible by 3.

6. Check Which numbers are evenly divisible by 5? 7,593,494,309,345 2494 90 Yes! No! Yes!

7. Check Which numbers are evenly divisible by six? 634 9360 442 No! Yes! No!

8. Choosing the Operation Focusing on Step 3 Pay attention to key words and phrases that may suggest the type of calculation you need to do to solve the problem.

9. Example 1 Ruby makes $720 a week, and her daughter Marie makes $360. What is their combined weekly income? Question: What is their combined weekly income? Operation: key word- combined; add Ruby and Marie’s income $720 + $360 = $1080

10. Example 2 A freight elevator can hold 2500 pounds. A table saw weighing 375 pounds is loaded onto the elevator. How much more weight can the elevator hold? Question: How much more weight can the elevator hold? Operation: keyword- how much more; Subtract the weight of the saw from the total weight the elevator can hold. 2500-375 = 2125pounds

11. Example 3 Mark’s gross monthly salary is $3,000. His employer withholds $600 for taxes and social security. What is Mark’s net salary each month? Question: What is Mark’s net salary each month? Operation: keyword- withholds; Subtract the amount withheld from the gross salary Solution: $3000-$600= $2400

12. Example 4 On a highway Jack can drive 24 miles on 1 gallon of gasoline. How far can he drive with 10 gallons of gas? Question: How far can he drive with 10 gallons of gas? Operation: keyword- of; Multiply the rate of 24 miles on 1 gallon by 10 gallons Solution: 24mpg x 10 g = 240 miles

13. Example 5 Last year the Soto family paid $4800 in rent. What was their monthly rent? Question: What was their monthly rent? Operation: keyword- monthly (per month); Divide the yearly rent by 12. Solution: $4800 ÷ 12 = $400

14. Example 6 One carton contains 24 cans of tomatoes. How many cartons are used to hold 400 cans of tomatoes? Question: How many cartons are used? Operation: keyword: none; Divide 400 by 24, the number of cans in one carton Solution: 400 ÷ 24 = 16 with 16 cans remaining. SO, you will need 17 cartons to hold all the cans.

15. Practice Solve the problems in Exercise 3 by writing the question, the operation, and finding the solution in the spaces provided.