Singapore Grade 3 mathematics question

[bernard2012]

Hi Experts,
Can anyone help me with the formula for the following question? Thanks in advance.

Q) Mr. Smith bought a total of 50 notebooks and scissors for $154. He paid $5 for each notebook and $2 for each pair of scissors.
a) How many pairs of scissors did he buy?
b) How many notebooks did he buy?

answers : a = 32 b = 18

 

[Deleted member 4993]

Hi Experts,
Can anyone help me with the formula for the following question? Thanks in advance.

Q) Mr. Smith bought a total of 50 notebooks and scissors for $154. He paid $5 for each notebook and $2 for each pair of scissors.
a) How many pairs of scissors did he buy?
b) How many notebooks did he buy?

answers : a = 32 b = 18

Since the problem is posted in Arithmetic forum (and for 3 rd. grade), we will use trial&error method.
To start we will assume we bought

25 note books and 25 scissors. How much money was spent?

= 25 * 2 + 25* 5 = 175

That is more than 154 alloted. So we reduce no. of notebooks (more expensive) and increase no of scissors. Let us try 20 notebooks and 30 scissors. What would be the total cost then?

Adjust accordingly and continue ....

 

[bernard2012]

Since the problem is posted in Arithmetic forum (and for 3 rd. grade), we will use trial&error method.
To start we will assume we bought

25 note books and 25 scissors. How much money was spent?

= 25 * 2 + 25* 5 = 175

That is more than 154 alloted. So we reduce no. of notebooks (more expensive) and increase no of scissors. Let us try 20 notebooks and 30 scissors. What would be the total cost then?

Adjust accordingly and continue ....

Thank you very much.

 

[Dr.Peterson]

Hi Experts,
Can anyone help me with the formula for the following question? Thanks in advance.

Q) Mr. Smith bought a total of 50 notebooks and scissors for $154. He paid $5 for each notebook and $2 for each pair of scissors.
a) How many pairs of scissors did he buy?
b) How many notebooks did he buy?

answers : a = 32 b = 18

Another fairly elementary method is to make a guess and then directly modify it into a solution.

Suppose all 50 items were scissors. What would be the total cost? $100

How much more needs to be spent to reach $154? $54

How much more will you spend if you replace a pair of scissors with a notebook? $3

How many times do you have to do that to reach $154? 54/3 = 18; so we need 18 notebooks.

 

[bernard2012]

Got it..very clear explanation. Thanks a lot

 

[HallsofIvy]

Hi Experts,
Can anyone help me with the formula for the following question? Thanks in advance.

Q) Mr. Smith bought a total of 50 notebooks and scissors for $154. He paid $5 for each notebook and $2 for each pair of scissors.
a) How many pairs of scissors did he buy?
b) How many notebooks did he buy?

answers : a = 32 b = 18

"a= 32 b= 18" makes no sense at all because you haven't said what "a" and "b" represent. If you mean that he bought 32 pairs of scissors and 18 notebooks, say that!

 

[JeffM]

"a= 32 b= 18" makes no sense at all because you haven't said what "a" and "b" represent. If you mean that he bought 32 pairs of scissors and 18 notebooks, say that!

Halls, those are not variables. They are the labels of the questions for which 32 and 18 are the respective answers.