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Ok, I have a few mental mathematics tricks which are really useful! Here is one:
It is also one of the easiest strategies because it is based on the memorizing of only nine numbers. To be able to extract the cube of a cube root you have to know the following chart from memory.
1 3 = 1
23 = 8
33 = 27
43 = 64
53 = 125
63 = 216
7 3 = 343
83 = 512
93 = 729
Notice the last digit in each answer shown above is underlined, and notice that each answer ends in a different digit. What this means is that no answer when numbers 1-9 are cubed will end in the same digit. Now with this bit of information let's look at this example:
The last digit in the second part of the answer is a 6. Look at the chart on the top of the page, and
tell me which number when cubed ends in a 6?
The answer is 6 because 6 3=216. Now you know the second half of the answer is '6'.
To figure the first part of the answer, just look at the whole number to the left of the comma. In this case it is 175. Now look at the answers to 1-9 cubed. Between what two numbers does the number 175 fit? Right, between 125 and 216. You always use the smaller of the two numbers which the whole number falls between, so in this case it would be 5.
Memorizing this chart is easy and very useful!
Figure out these next cubed roots for yourself. Use the chart on the first three problems and try the
remaining problems without the chart.
704,969 - 778,688 - 85,184 - 24,389 - 262,144 - 551,368 - 681,472 - 970,299 - 314,432
*The '3' written in front of single numbers is the sign of cube. E.g. '93' is not ninety three, it's 9 to the power 3.
Deriving a cube root in mind within seconds (No matter how large the number)!
This strategy is good to show off with because no one would believe you could figure these equations in your head! It is also one of the easiest strategies because it is based on the memorizing of only nine numbers. To be able to extract the cube of a cube root you have to know the following chart from memory.1 3 = 1
23 = 8
33 = 27
43 = 64
53 = 125
63 = 216
7 3 = 343
83 = 512
93 = 729
Notice the last digit in each answer shown above is underlined, and notice that each answer ends in a different digit. What this means is that no answer when numbers 1-9 are cubed will end in the same digit. Now with this bit of information let's look at this example:
563 = 175,616
Split the answer in half, always at the comma, to get 175 | 616.The last digit in the second part of the answer is a 6. Look at the chart on the top of the page, and
tell me which number when cubed ends in a 6?
The answer is 6 because 6 3=216. Now you know the second half of the answer is '6'.
To figure the first part of the answer, just look at the whole number to the left of the comma. In this case it is 175. Now look at the answers to 1-9 cubed. Between what two numbers does the number 175 fit? Right, between 125 and 216. You always use the smaller of the two numbers which the whole number falls between, so in this case it would be 5.
Memorizing this chart is easy and very useful!
Figure out these next cubed roots for yourself. Use the chart on the first three problems and try the
remaining problems without the chart.
704,969 - 778,688 - 85,184 - 24,389 - 262,144 - 551,368 - 681,472 - 970,299 - 314,432
*The '3' written in front of single numbers is the sign of cube. E.g. '93' is not ninety three, it's 9 to the power 3.
