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### Course: Pre-algebra>Unit 8

Lesson 2: Rational number word problems

# Rational number word problem: computers

In this word problem, we'll compare the weight of two objects using a ratio of integers. We'll practice simplifying a fraction, too. Created by Sal Khan.

## Want to join the conversation?

• is the information in the question accurate??
• The weight of the computers is accurate. The Mark I (1944) (Harvard University's electro-mechanical computer) weighted 4,500kg and was 16 meters in length and 2.4 meters tall. Today some laptops like the MacBook Air weight as little as 1.08kg.
• What's a ratio? I haven't been taught this.
• A ratio is a comparison between two quantities. It can written as a : b, a to b, or a/b, where a and b can be any number.
• I don't understand what you mean as an integer is a whole number, like 1, -2, 12, -5? is there another way to explain this?
• Integers are zero, positive number and negative numbers, but no fractions or decimals.
so: 0, 1, 2, 3, 4, 5, 6, 7, ... etc.
and -1, -2, -3, -4, -5, -6, -7, .... etc.
• Every fraction a rational number but why is every rational number not a fraction?
example
-2 is a rational number so we can express it as -2/1 which is a fraction
• Every rational number can be be represented as a fraction, but not every rational number must be represented as a fraction.
• So integers can ONLY be whole numbers? So does that mean decimals and fractions are NOT integers?
• Yep, decimals and fractions are forbidden from being an integer.
• I thought for fractions you can't have decimals for either numerator or denominator
• you can have decimals in the numerator and the denominator
• Why is the ration expressed as 5000/3 and not as 3/5000? Is there a rule?
• Because we were asked to give a ratio of the weight of the old computers to the weight of the new ones. If we were asked new to old, it would be 3/5000. Basically, the first case (the one in the video) shows us how much the old computers were heavier then the new ones, and the other would show how much the new ones are lighter than the old. It's essentially the same thing, just a different point of view.
• How would you solve this:
Sally's basked has a hole in it. For every 292 steps she takes, the hole widens by 5mm. How much would the hole have widened after 146 steps?
• You would cut the amount it widens by half, since she only walked half the time it takes to cut 5mm (half of 292 is 146). Half of 5 is 2.5. So it widened by 2.5 mm.