Question 1119831
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A solution using formal algebra, like the one provided by the other tutor, is of course a good exercise.<br>
But if the question is on a competitive exam where speed is important, the problem can be solved far more quickly with a little logical analysis and some easy mental arithmetic.<br>
(1) If Jenny was 10 times as old as Rose 5 years ago, then their ages then must have been 10 and 1, or 20 and 2, or 30 and 3, or ....<br>
(2) Then their ages now must be 15 and 6, or 25 and 7, or 35 and 8, or ....<br>
(3) Then their ages 3 years from now must be 18 and 9, or 28 and 10, or 38 and 11, or ....<br>
Of course, you can stop with that first pair, because it satisfies the required condition that in 3 years Jenny will be twice as old as Rose.<br>
And of course to answer the second question you simply find the difference in their ages -- either 5 years ago, or now, or 3 years from now.