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Score to pass: 70%
1. 10 MCQs on expressing ratios in simplest form
2. 10 MCQs on multipliers for proportional change
3. 10 MCQS on properties of proportions
There are two types of proportional change. One is the increase and the other is decrease. The best way to deal with the proportional change is to first of all know that each quantity before change has 100%. Then, if there is an increase the new percentage becomes greater than 100%. If there is a decrease, then we have the new percentage less than 100%.
Steps to calculations of proportional change using multiplier
There is a few steps to calculations of proportional change using multiplier that we want to highlight. But, we use two methods.
Method 1: Calculating the multiplier
Step 1: Decide the increase or decrease
After reading the problem and understand it, you need identify if we have an increase or a decrease.
Step 2: Calculation of new percentage and multiplier
If there is an increase, then we have to add the percentage increase to 100%.
If there is a decrease then we have to subtract the percentage decrease from 100%.
Step 3. Calculate the new quantity
The value of the new quantity is equal to the original quantity multiply the multiplier.
Example: In 2004 a miller processed 800 tonnes of maize. In 2005, the miller decreased production by 30 %. How many tonnes did the miller process in 2005?
Solution
Step 1: The word decreased production means that there is a decrease change.
Step 2: The new percentage after decreased is 100%-30%=70%=0.7
Step 3: The new production in 2005 is 800 tonnes multiply 0.7, which gives us 560 tonnes.
Method 1: Step by Step Method
Step 1: Decide the increase or decrease
Based on the understanding of the problem, we identify whether there is an increase or decrease.
Step 2: Calculation of the increase or decrease amount
Whether there is a decrease or increase, the amount changed is equal to orginal quantity multiply by the percentage change.
Step 3: Calculate the new quantity
If there is an increase, then new amount becomes the original plus the amount change.
If there is a decrease, then new amount becomes the original minus the amount change.
Example. We use the above example
Step 1: It is a decrease change
Step 2: The amount changed is 800 tonnes multiply by 0.3 which is 240 tonnes.
Step 3: The new production is 800 tonnes - 240 tonnes = 560 tonnes.