The Robin Hood Equation

Quick! Try the following example, without thinking about it:

Set up an equation for the statement “there are twice as many bananas as apples”

Is it 2B = A or 2A = B?

If we use some numbers we can see which equation works. Since there are twice as many bananas we can use the numbers 4 and 2. If there are 2 apples there are twice as many bananas, so 4 bananas. If you put these numbers into the possible equations you can see which one works. Substitute 4 for B and 2 for A and we see that the second equation works. 2A = B becomes 2*2 = 4.

But how can we get to the correct equation without having to think of plugging in numbers? Take the example from the OG :

“Lois has x dollars more than Jim has”

You might want to say “L + x = J” this seems to make sense because Lois has more dollars. But that is not correct. To always set up your equations correctly think about what Robin Hood would do.

Robin Hood is the famous outlaw known for “Robbing the rich to pay the poor.” Now before you start making jokes about socialism remember that in the Robin Hood stories the law was corrupt and by taking from the rich he was only making things more equal. That is what you need to do make things equal! So just do it the way Robin Hood would do it — either take from the rich OR give to the poor. Remember that an equation means things have to be equal… Since Lois has more dollars we have to take some away from her OR give some to Jim. So “L – x = J” or “L = J + x.”

Whichever person or variable has more is the one that you need to take from and the one that has less is the one that you need to give to.

Take from the rich:
If “Allan has y dollars more than Bob” then Allan has more and to make it equal we need to take from the rich. So the equation is “A – y = B”

Give to the poor:
So if “Tom has 5 less than Sarah” we see that Tom has less and we need to give him more to make things equal. So the equation is “T +5 = S.”

Try these examples:
1. “There are 6 times as many dogs as there are cats”
2. “If John had $700 less he would have 3 times the amount of money that Brian has.”

Answers:
1. Since the dogs are the rich we have to give to the poor – the cats. So “D = 6C”
2. The first part of this is straightforward, it is “J- $700” which is if John had $700 less…now we have to give to the poor which is Brian. So the answer is “J-$700 = 3B”

Whenever you come across a GMAT equation that is unequal, act like Robin Hood (or a good socialist) and even things up, “Take from the Rich OR Give to the Poor” and you will never go wrong.

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