Front-End Estimation
Use front-end estimation to find:
545 + 281
Best answer: 700
Use overestimation to find:
545+281
Best answer: 900
Use true rounding to find:
545+281
Best answer: 800
Use compatible numbers to find:
28xx6
Lot's of choices, including:
30xx6=180
30xx5=150
At the store, you bought 5 chocolate bars for you and some friends. Each bar cost $1.75. What bill should you use to minimize the amount of change you get back?
A $10 bill. The total cost is less than $10 (overestimate is 5 x $2 = $10) but defintely more than $5 (underestimate is 5 x $1 = $5)
How do we use front-end estimation?
a) round the answer to the front number
b) round the front number down before you do the computations
c) round to the nearest whole number
b) You always round to the front number(s) before you do the computations. We call this the "round down" strategy. It's the fastest because you just use the numbers you see.
Use front-end estimation to find:
842 - 388
Best answer: 500
Use overestimation to find:
842 - 388
Best answer: 500
Use true rounding to find:
842-388
Best answer: 400
Use compatible numbers to find:
83-:11
Lot's of choices, including:
80-:10=8
88-:11=8
84-:12=7
Six friends found a $100 bill and decided to split it between them. About how much does each get?
Two examples include:
100 / 5 = $20
90 / 6 = $15
(lots of possibilities though!)
True or False: Overestimation is when you round all of the numbers up for a calculation.
True. By rounding everything up, you'll always overestimate the actual answer. This is a good strategy for shopping at a grocery store!
Use front-end estimation to find:
382 + 1249
Best answer:1500
Use overestimation to find:
382 + 1249
Best answer: 1700
Use true rounding to find:
382+1249
Best answer: 1600
Use compatible numbers to find:
42xx31
Lots of choices, including:
40xx30=1200
50xx30=1500
At a restaurant, a family ordered 5 burgers for $8.75 each, 2 small fries for $3.50 each, 3 onion rings for $4.25 each and 5 soft drinks for $3.75 each. Approximately how much is the total cost of the order? (No taxes or tip)
Overestimate: $95
Underestimate: $73
(So somewhere in between.)
a) round all numbers down
b) round all numbers up
c) round numbers with a 0 to 4 down and numbers 5 to 9 up
c) for best answers, you can even round some up and some down to get closer to the real answer
Ex. 452 + 351 --> 500 + 300 = 800
Use front-end estimation to find:
291+812+438+711
Best answer: 2100
Use overestimation to find:
291+812+438+711
Best answer: 2500
Use true rounding to find:
291+812+438+711
Best answer: 2200
Use compatible numbers to find:
131-:11
Lot's of choices including:
132-:11=12
130-:10=13
130-:13=10
If you can run about 4 km in 18 minutes, about how fast can you run?
about 12 km/h
- there are about three "18 minutes" in an hour (3x4=12)
True or False: Rounding can be used as an estimation strategy, but it's used more commonly to shorten final answers after a calculation is made.
TRUE. We most often use rounding when we get decimal answers that have too many (and unnecessary) decimal places.
Use front-end estimation to find:
818 - 126 + 455
Best answer: 1100
Use overestimation to find:
818 - 126+455
Best answer: 1200
Use true rounding to find:
818-126+455
Best answer: 1200
Use compatible numbers to find:
3550.19-:68.2
Lot's of choices, including:
3500-:70=50
3600-:60=60
4000-:80=50
A soup can is 11.5 cm tall and it's diameter is 7.5 cm. Approximately, what is the volume of the can in cm3?
There's a lot of ways to do this, but
V=pi r^2h
V=3xx4^2xx10
V=3xx16xx10
V=480cm^3
Which best describes estimation:
a) Getting a quick guess that is close to the real answer
b) Working to calculate a number that is only a few numbers away from the real answer
c) A blind guess that you hope is close to the real answer
a) A good estimate will be quick and get you close to the real answer. If you can't do it quick and in your head, it's not a good estimate for you!