Lesson 102: Real-world: Exact or Approximate

Sometimes an exact answer is needed when an approximate answer is not close enough

This is not just in math class, but in the real world.

SORT CARDSWhich situations will require an actual amount or an estimate?

Exact Approximate

Cups in a recipe Gallons in a lake

Exact amount of gas a car holds Amount of cake needed for a birthday party

Kilometers to finish a race ‘Sporks’ the cafeteria orders to make sure there is enough

Yards on a football field The number of blow fish in the ocean

Minutes in each music class Amount of spaghetti to boil for a family of four

People who voted in an election Milk consumed by the average 5th grader in one year (at home & school)

Square feet of carpet for a bedroom

The amount of food the cafeteria prepares each day for the whole school district

Actual ounces in a milk jug How much money is needed to buy groceries

Sometimes we will need to know which is the

BEST way to estimate

A. Round each amount to the nearest $100,

then subtract to find the difference

B. Round each amount to the nearest $10,

then subtract to find the difference

C. Subtract the amounts, then round the difference to the nearest $10

D. Subtract the amounts, then round the difference to the nearest $1

A. Adding $10.00 a total of nine times

B. Thinking $9.00 x 9 and $1.00 x 9 and

then adding them together

C. Multiplying twelve by $9.00

D. Multiplying nine by $10.00

Carrie ESTIMATED the sum in the problem by rounding each number to the nearest thousand before adding. Which should

have been Carrie’s ESTIMATE?

The answer would be….B. 51,000

How could Carrie get the incorrect answers?

46,00056,00052,000

Bobby wants to ESTIMATE the sum of problem by rounding each fraction to the nearest

whole number before adding. Which should be his

ESTIMATE?

The answer would be: C. 27

Talk with a shoulder partner about HOW you would solve this problem.

A. Add the amounts, round to the nearest $100, and then multiply by 5

B. Round each amount to the nearest $100, add, and then multiply by 5

C. Add the amounts and then round to the nearest $100

D. Round each amount to the nearest $100 and then add

With a shoulder partner, think of some words in a problem that tell you they want an EXACT answer

How manyTotal costExactly or exactHow muchActual

A. 35,058B. 34,058C. 40,000D. 35,057

B. 34,058

Time out: THINK – how would you solve it?PAIR – with neighborBe ready to SHARE!

A. 195 ½ inchesB. 200 inchesC. 195.9 inchesD. 196

C. 195. 9

A. $16.31B. $33.69C. $44.69

D. $33.68

B. $33.69

What mistake was made to get:

A.$16.31C.$44.69D.$33.68

Independent practice page

Journal: Write how you would estimate the sum of 7,345 and 3,942. What method would you use?