Transcript File

Main Idea and New Vocabulary
Example 1: Estimate by Rounding Dividends
Example 2: Estimate by Rounding Divisors
Example 3: Real-World Example
Example 4: Real-World Example
• Estimate the quotient of decimals and judge the
reasonableness of the results.
• compatible numbers
Estimate by Rounding Dividends
Estimate 44.2  9.
Using multiples of 9, 44.2
is closest to 45.
Answer: The quotient is about 5.
Estimate 58.8  6.
A. 48 ÷ 6 = 8
B. 54 ÷ 6 = 9
C. 60 ÷ 6 = 10
D. 66 ÷ 6 = 11
Estimate by Rounding Divisors
Estimate 72  8.3.
Round 8.3 to 8 since 72
and 8 are compatible
numbers.
Answer: So, 72 ÷ 8.3 is about 9.
A.
60 ÷ 6 = 10
B.
54 ÷ 9 = 6
C.
60 ÷ 12 = 5
D.
60 ÷ 10 = 6
MAMMALS The average weight of a Florida
panther is 64.2 kilograms. The average weight of
a coyote is 14.8 kilograms. About how many
times heavier is the panther? Explain why your
answer is reasonable.
Round 14.8 to 15 and 64.2
to 60 since 15 and 60 are
compatible numbers.
Answer: The panther is about 4 times heavier than
the coyote.
Check for Reasonableness Since 4 × 15 = 60 and
60 is close to 64.2, the
answer is reasonable.
PUPPIES In a study, the average weight of a
6-week old male Labrador Retriever puppy was
5.63 kilograms. The average weight of the same
puppies at 20 weeks old was 17.89 kilograms. By
about how many times did the average weight
increase from 6 to 20 weeks old?
A. about 2 times
B. about 3 times
C. about 4 times
D. about 5 times
TRAVEL The Chu family drove 163.35 miles in
4 hours. Estimate the average number of miles
they drove each hour. Justify your answer.
Round 163.35 to 160.
Answer: The Chu family drove about 40 miles each
hour.
Check for Reasonableness Since 40 × 4 = 160
and 160 ≈ 163.35, the
answer is reasonable. 
GAS MILEAGE The Mays family drove 148.5 miles
using 5 gallons of gas. Estimate the number of
miles they drove for each gallon of gas.
A. about 20 miles
B. about 30 miles
C. about 50 miles
D. about 450 miles