Question 1210341
Too many asked at once.  I will only do #10.


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10. A man is 5 times as old as his son. In 15 years, he will be twice as old. How old are they now?
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m, the man's age now
m/5, his son's age now


The second sentence means exactly {{{m+15=2m}}}.
You did not specify without amiguity.


{{{0+15=2m-m}}}

{{{m=15}}}