p = price for a pair of leather shoes
q = price for a pair of canvas shoes
m = the total price for Andi's order

Andi's order: 5p + aq = m    (1)
p = 2.5q                             (2)
12.5q + aq = m                   (3) substitute (2) into (1)

Andi's assistant's order: ap + 5q = m + m/3  (4)
2.5aq + 5q = 4m/3                                      (5) simplify (4)
7.5aq + 15q = 4m                                       (6) (5) times 3

4aq + 50q  = 4m                                         (7) (3) times 4
3.5aq - 35q = 0                                           (8) subtract (7)
from (6)
q (3.5a - 35) = 0                                          (9) separate q
for factorization
q != 0                                                         (10) price
can't be 0
3.5a - 35 = 0                                               (11) this part
of (9) is the cause of (9)
a = 10                                                         (12) easily
obtained from (11)

Therefore,

ratio = 5:a = 5:10 = 1:2

-- 
Abu 'Abdirrahman, Ahmad Ridha bin Zainal Arifin bin Muhammad Hamim
(l. 1400 H/1980 M)

-- 
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