Q&A - PSLE Math
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liketoeat:
First 100 odd numbers --->Will question like the following appear in PSLE? Could someone pls help to solve. Thank you.
Find the sum of the digits of the first 100 odd numbers. (Ans = 1000)
01,3,5,7,9,11,13,15,17,19 (10 odd numbers)
21,.........31,..............39 (20 odd numbers)
41,.............51...........59 (30 odd numbers)
:
101
121
141
161
181...........................199 (100 odd numbers)
(1+3+5+7+9) = 25
1*5 + 25 = 30
2*5 + 25 = 35
3*5 + 25 = 40
:
:
:
9*5 + 25 = 70
1*5 + 0*5 + 25 =30
1*5 + 1*5 + 25 = 35
1*5 + 2*5 + 25 = 40
:
:
:
1*5 + 9*5 + 25 = 75
Total = 25 +(30 + 35 + .......+70 + 30 + 35 + ..+ 70)+75
= 25+75 + (450*2)
= 100 + 900
=1000 -
liketoeat:
HiWill question like the following appear in PSLE? Could someone pls help to solve. Thank you.
Find the sum of the digits of the first 100 odd numbers. (Ans = 1000)
I'd like to find out if you are talking about the sum of these consecutive odd numbers like
1,3,5,7,9 ...............191,193,195,197,199
I am asking beacause your question shows sum of digits, like 8 is one digit and 88 is two digits.
Usually, the question is asked as
Find the sum of the first 100 odd numbers.
If this is the case, the answer is 10000.
Best wishes -
tianzhu:
I find this question funny as well, I think its asking about the digits...then it will become very tedious to work out, right? I think it won't come out in PSLE!
Hiliketoeat:
Will question like the following appear in PSLE? Could someone pls help to solve. Thank you.
Find the sum of the digits of the first 100 odd numbers. (Ans = 1000)
I'd like to find out if you are talking about the sum of these consecutive odd numbers like
1,3,5,7,9 ...............191,193,195,197,199
I am asking beacause your question shows sum of digits, like 8 is one digit and 88 is two digits.
Usually, the question is asked as
Find the sum of the first 100 odd numbers.
If this is the case, the answer is 10000.
Best wishes -
ksi:
Wow, will it come out in PSLE? Thank you.
First 100 odd numbers --->liketoeat:
Will question like the following appear in PSLE? Could someone pls help to solve. Thank you.
Find the sum of the digits of the first 100 odd numbers. (Ans = 1000)
01,3,5,7,9,11,13,15,17,19 (10 odd numbers)
21,.........31,..............39 (20 odd numbers)
41,.............51...........59 (30 odd numbers)
:
101
121
141
161
181...........................199 (100 odd numbers)
(1+3+5+7+9) = 25
1*5 + 25 = 30
2*5 + 25 = 35
3*5 + 25 = 40
:
:
:
9*5 + 25 = 70
1*5 + 0*5 + 25 =30
1*5 + 1*5 + 25 = 35
1*5 + 2*5 + 25 = 40
:
:
:
1*5 + 9*5 + 25 = 75
Total = 25 +(30 + 35 + .......+70 + 30 + 35 + ..+ 70)+75
= 25+75 + (450*2)
= 100 + 900
=1000 -
Actually it is not tedious to work out, there is a pattern to calculate everything quite fast, I present more details for you to see but in exam, this can be done in 4 lines.
Having said this, this is more MO type of questions. However, I notice selective MO type of questions are getting into the PSLE as well. -
I've been struggling
with my DD h'wk....Pls help..
(1) Mr Mohn bought a certain number of cameras and watches for $1980.
Each camera cost $60. Each watch cost 1/4 as much as a camera.
If 40% of the items he bought were cameras, how many watches
did he buy?
(2) $400 were shared by 4 boys. Alan received 25% of the total amount
that Ben, Carl and Dan received. Ben's share was 60% of the
amount received by Carl and Dan. Carl received 4 times as much
as Dan. How much more did Ben receive than Dan? -
ksi:
Hi ksiActually it is not tedious to work out, there is a pattern to calculate everything quite fast, I present more details for you to see but in exam, this can be done in 4 lines.
Having said this, this is more MO type of questions. However, I notice selective MO type of questions are getting into the PSLE as well.
From your earlier details,it appears that you are calculating the sum of the first 100 odd numbers from
1+3+5+7+9 + ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦..191,193,195,197,199
Am I right to say that?
Best wishes -
tianzhu:
Hi Tianzhu,
Hi ksiksi:
Actually it is not tedious to work out, there is a pattern to calculate everything quite fast, I present more details for you to see but in exam, this can be done in 4 lines.
Having said this, this is more MO type of questions. However, I notice selective MO type of questions are getting into the PSLE as well.
From your earlier details,it appears that you are calculating the sum of the first 100 odd numbers from
1+3+5+7+9 + ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦..191,193,195,197,199
Am I right to say that?
Best wishes
1+3+5+7+9 = 25 is common for all the first 100 odd numbers.
So I calculated this to be the constant 25 for each series of number with a different 1-digit and 2-digits starting.
1 digit starting...the adding pattern is 1*5, 2*5, 3*5 etc....9*5
2-digit starting....the adding pattern is 1*5+0*5, 1*5+1*5, 1*5+2*5,..... and this pattern can be further simplied.
So the constant is to be added for each series. -
[quote=\"sexymama\"]I've been struggling
with my DD h'wk....Pls help..
(1) Mr Mohn bought a certain number of cameras and watches for $1980.
Each camera cost $60. Each watch cost 1/4 as much as a camera.
If 40% of the items he bought were cameras, how many watches
did he buy?
Suggest use guess and check:
Camera - $60, Watch - $15
Camera is 40% and watch is 60% of total purchase
Camera Watch Total
4 x $60 6 x $15 = $330
12 x $60 18 x $15 = $990
24 x $60 36 x $15 = $1980 (Correct Answer)
Mr Mohn bought 36 watches.
Hope the answer is correct.
:lol: -
ksi:
Hi Tianzhu,
Hi ksitianzhu:
[quote=\"ksi\"]Actually it is not tedious to work out, there is a pattern to calculate everything quite fast, I present more details for you to see but in exam, this can be done in 4 lines.
Having said this, this is more MO type of questions. However, I notice selective MO type of questions are getting into the PSLE as well.
From your earlier details,it appears that you are calculating the sum of the first 100 odd numbers from
1+3+5+7+9 + ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦ā¦..191,193,195,197,199
Am I right to say that?
Best wishes
1+3+5+7+9 = 25 is common for all the first 100 odd numbers.
So I calculated this to be the constant 25 for each series of number with a different 1-digit and 2-digits starting.
1 digit starting...the adding pattern is 1*5, 2*5, 3*5 etc....9*5
2-digit starting....the adding pattern is 1*5+0*5, 1*5+1*5, 1*5+2*5,..... and this pattern can be further simplied.
So the constant is to be added for each series.[/quote]Hi ksi
If you are calculating the sum of the first 100 odd numbers, the answer is unlikely to be 1000.
Take for example, the sum of the last few first 100 odd numbers
181+183+185+187+189+191+193+195+197+199
They almost add up to 1000 already.
Best wishes
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