51.--HOW OLD WAS MARY?

The age of Mary to that of Ann must be as 5 to 3. And as the sum of

their ages was 44, Mary was 27½ and Ann 16½. One is exactly 11 years

older than the other. I will now insert in brackets in the original

statement the various ages specified: "Mary is (27½) twice as old as Ann

was (13¾) when Mary was half as old (24¾) as Ann will be (49½) when Ann

is three times as old (49½) as Mary was (16½) when Mary was (16½) three

times as old as Ann (5½)." Now, check this backwards. When Mary was

three times as old as Ann, Mary was 16½ and Ann 5½ (11 years younger).

Then we get 49½ for the age Ann will be when she is three times as old

as Mary was then. When Mary was half this she was 24¾. And at that time

Ann must have been 13¾ (11 years younger). Therefore Mary is now twice

as old--27½, and Ann 11 years younger--16½.

Amusements in Mathematics · 第 555 / 970 题