Making Sense of
Sensible (?!?) Rounding
Jojo Uichanco / Lukas van Veen
“How much?”
“HOW MUCH?”
involves a form of measurement :
no sensible rounding necessary.

How much did he spend?
How much sleep did you get?


“How many?”
Answer “HOW MANY?”
with a WHOLE number by rounding sensibly.

How many students does it take to change a
light bulb?
The framework


Sensible rounding always asks:
“How many?”
Need in the problem  Round down
 Need in the question  Round up
Example 1.

A taxi can carry up to four passengers.
How many taxis do we need to carry 13?
13 ÷ 4 = 3.25

Round down or up?
3.25
Can 3 taxis carry 13 students?
3 x 4 = 12 students
Need is in the question: round up
4 taxis can carry 13 students
Example 2.
Let’s make (or bake) a cake

Hessa needs four eggs to make a cake.
How many cakes can she make with 11
eggs?
11 ÷ 4 = 2.75
2.75
Can Hessa make three cakes?
3 cakes x 4 eggs  12 eggs
Need is in the problem: round down
With 11 eggs Hessa makes 2 cakes
Example 3.

I need five meters to make a dishdasha.
How many dishdashas can I make
with 14 meters?
14 ÷ 5 = 2.8
Two or three?
Need is in the problem: round
down

I can make 2 dishdashas
Watch out!!!

A pizza is cut into six slices.
Khalid has 20 slices.
How many pizzas does Khalid have?


3 1/3
A pizza is cut into six slices.
Khalid has 20 slices.
How many whole pizzas does Khalid have?

3
Watch out!!!


A box holds twelve eggs.
How many boxes are needed for 25 eggs?
Round up: 3
A box holds twelve eggs. How many
full boxes can be made with 25 eggs?
Round down: 2