Estimation strategies - Lesson 4

in #mathematics6 years ago

Estimation strategies of decimals:

Image source

Decimal estimations 

Considering the following situations, we will discuss 5 strategies for estimating the answers. 

In each discussion, an example will be given:

Image source 

1. Peter’s mother sends him to the shop to buy sugar, cool drink and sweets.  The sugar cost R 39,99 the cool drink is R15,76 and the sweets costs R 41,45.  His mother only gave him R 100.  How can Peter avoid embarrassment at the till?  How can he estimate if he has enough money? 

Strategy 1

Round up and use compatible  numbers 

R 39,99 is close to R40, R 15,76 can be rounded off to R 20 and R41,45 can be rounded off to R40 too.  

If we add: R40 + R20 + R40 =R100.  

As this estimation is overestimated, Peter will have enough money to pay for the items. 

2. Determining savings:

Image source

A building contractor has to replace the roof of a building that was damaged by winds.  He calculates that the roof will need 12 roof sheeting’s.  He goes to two different stores to get quotations on the roof sheeting’s.  One store asks R19,45 per sheet and the other store R 24,30 per sheet.  Calculate how much money the contractor will save if he buys the roof sheeting’s at the cheaper store. 

Strategy 2

You could try to estimate 12 x R19,45 and 12 x R24,30 and then subtract the two answers from each other.  You will realize that if you round of both the prices, and subtract them from each other and then multiply the answer with 12, you will also get an estimated answer. 

Therefore, 24 – 20 = 4.  4 x 12 =R 48.  The builder will save an estimated amount of R 48.  

 

Image source

3. A farmer wants to sell one of his tractors he bought in 2004,the tractor is now valued at R100000 which is two times what he paid for it 14 years ago. How much did he pay for the tractor in 2004? 

Current price x 2 = R100 000 which gives us the buying price as 10000÷ 2 =? 

Strategy 3

Use the guess-check-improve strategy 

Guess 1:  20 000 + 20 000 = 40 000 which is too small.  

Guess 2:  60 000 + 60 000 = 120 000 which is too much.

Guess 3:  50 000 + 50 000 = 100 000 which is the correct answer. 

This means that the buying prices of the tractor was R 50 000.

Strategy 4

Use compatible numbers and determine the upper and lower bounds.

100 000 ÷ 3 = 33 333 and 100 000 ÷ 2 = 50 000 Therefore: 33 333 + 50 000 = 83 333 ÷ 2 = R 41 6667 

4.  How long will it take??  

Image source

An athlete is running at a speed of 6,9 m/s,  At this rate,  how long will it take the athlete to run 200m? 

Strategy 5 

6,9 ≈ 7  therefore 28 x 7 = 196 and 29 x 7 = 203.  This means that the athlete will run the 200m in about 28 to 29 seconds.


Sort:  

You got a 2.52% upvote from @postpromoter courtesy of @apteacher!

Want to promote your posts too? Check out the Steem Bot Tracker website for more info. If you would like to support the development of @postpromoter and the bot tracker please vote for @yabapmatt for witness!

Coin Marketplace

STEEM 0.35
TRX 0.12
JST 0.040
BTC 70733.96
ETH 3563.16
USDT 1.00
SBD 4.76