Define: Before you add or subtract decimals, what must you do?
Define: Steps to changing the power of 10 in SN:
Define: Words that tell you to subtract:
#1: In 2012, the population of NY was about 2.4 x 10^7 and the population of Oregon was 4 x 10^5. How many more people live in NY than in Oregon?
#2: 4.29 x 10^6 - 1.68 x 10^6=
#3: 5.08 x 10^-4 - 3.12 x 10^-5=
#4: A. 6 x 10^4 - 8 x 10^2=? and B. 6 x 10^4 - 0.08 x 10^4= ?
#5: In problem 4, what do you notice between the two answers?
Before you add or subtract decimals, you must make sure that the decimal points are lined up correctly.
Steps to changing the power of 10 in SN:
1. If the power of 10 is positive, move the decimal point to the right as many places as indicated by the power.
2. If the power of 10 is negative, move the decimal point to the left as many places as indicated by the absolute value of the power.
Words that tell you to subtract: minus, less than, fewer than, decreased by, difference
#1: To find how many more people live in NY than in Oregon, subtract the population of Oregon from the population of NY. (2.4 x 10^7) - (4 x 10^5) = 2.36 x 10^7.
#2: Subtract the given numbers with the same power of 10. (4.29 x 10^6) - (1.68 x 10^6) = 2.61 x 10^6.
#3: Subtract the given numbers with different powers of 10. (5.08 x 10^-4) - (3.12 x 10^-5) = 4.76 x 10^-4.
#4:
A. Subtract the numbers with the same power of 10. (6 x 10^4) - (8 x 10^2) = 6 x 10^4 - 0.8 x 10^3 = 5.992 x 10^4.
B. Subtract the numbers with different powers of 10. (6 x 10^4) - (0.08 x 10^4) = 5.92 x 10^4.
#5: In problem 4, you may notice that the answers are very close to each other, but the second answer is slightly smaller due to the subtraction of a smaller decimal (0.08) from a larger decimal (6).