Опубликовано 11.06.2017 по предмету Английский язык от Гость >> <<

Решите, пожалуйста, задание! Очень нужно!
The sum of ages of Tom and Elizabeth is 49. Tim is twice as old as Elizabeth was when Tom was as old as Elizabeth is now. How old are they?

Ответ оставил Гость

We have two moments of history here: "now" and "then" (at particular moment in the past). Lets mark as the following:
T - Toms age now
E - Elizabeths age now
To - Toms age then
Eo - Elizabeths age then

So we have:
T - E =  To - Eo (their difference is constant)   (1)
T + E = 49                                                         (2)
T = 2Eo                                                            (3)
To = E                                                               (4)

Using (4) into (1): 
T - E =  E - Eo  
Then using (3) here:
2Eo - E =  E - Eo  
2Eo + Eo =  E + E
3Eo =  2E
E = 3/2 Eo                                                         (5)

Using (5) and (3) into (2):
T + E = 49
2Eo + 3/2Eo = 49  
3 1/2Eo = 49
7/2Eo = 49
Eo = 49 : 7/2
Eo = 14

So, Elizabeth was 14. It means now Tom is 2*14=28. Elizabeth now is 49 - 28 = 21

Answer: Elizabeth is 21, Tom is 28