Singapore IP 3A ?? Help!

[Scuff]

We just started up IP again and I'm running into problems already! I can figure these out, but am at a loss on how to explain it or how they want the student to figure it out. So, help pls!

 

First problem: Topic 2, #25 The sum of 2 numbers is 100. The smaller number is 60 less than the bigger number. What is the smaller number?

And they have a bar chart with it showing 100= 60 + ? & bigger #

 

 

The answer is 20. With the bigger # being 80. But how does one firgure that out besides trial and error?

 

Second problem is similar. Topic 2, #26 The sum of the two numbers is 1000. The difference between them is 400. Find the larger number.

 

So 300 and 700, but again, is there a method to figuring this out??

[Jen500]

You can solve these using the bar method.

[Kate in Arabia]

Yes, bar diagrams are helpful.

 

For the first problem:

First problem: Topic 2, #25 The sum of 2 numbers is 100. The smaller number is 60 less than the bigger number. What is the smaller number?

 

The difference between the two numbers is 60. So:

 

first number = [XXXXX]

second number = [XXXXX] + 60

 

[XXXXX] + [XXXXX] + 60 = 100

 

Take out the 60, so the two equal-length bars =40. Divide by two, so one bar = 20.

 

first number = 20

second number = 20 + 60 = 80

 

 

Second problem is similar. Topic 2, #26 The sum of the two numbers is 1000. The difference between them is 400. Find the larger number.

 

This works the same way as above. You want to set it up so you have a bar, and figure out how many of these bars you need. In this example:

 

first number = [XXXXX]

second number = [XXXXX] + 400

 

first number + second number = 1000

[XXXXX] + [XXXXX] + 400 = 1000

 

Take away 400, and two equal-length bars = 600. So one bar equals 300.

 

first number = 300

second number = 300 + 400 = 700

 

hth!!