Place value can be used to subtract 4.23 and 2.75 because, in order to subtract, you must line up the whole numbers together, the tenths place together, and the hundredths place together.
Lining them up: Whole= W Tenths place= T Hundredths place= H
W T H
4 . 2 3
- 2 . 7 5
-------------------
1 . 4 8
Mrs Kennedy is buying pencils for 315 students.
The pencils are sold in boxes of 10.
Therefore the number of pencils she needs to buy should be a multiple of 10, so that she can buy boxes of 10 pencils each.
number of students are 315 but 315 is not a multiple of 10
so we have to round off 315 to the nearest ten, that's 320.
so then she has to buy 320 pencils
number of boxes she needs - 320 / 10 = 32 boxes of pencils
she only needs pencils for 315 students so she will have 5 extra pencils
she will have to buy 32 boxes
(4-3n-5n2)
+( -2+n-3n2)
____________________
-2-2n-8n2