Question 1153882
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A solution without formal algebra -- using logical reasoning and simple arithmetic instead....<br>
If the sum of their ages 10 years from now will be 50, then the sum now is 30.<br>
So the two ages are two whole numbers with a sum of 30 and a difference of 6.<br>
One way to solve this kind of problem quickly is to reason that the two numbers 15 and 15 have a sum of 30 but are the same; to get a sum of 30 with a difference of 6 between the two numbers, add 3 to one of the 15s and subtract 3 from the other -- giving you the numbers 18 and 12.<br>
ANSWER: Ben is 12; his sister is 18.<br>