Question 1199553
<br>
Once a month for 12 years means 12*12 = 144 deposits.<br>
The final amount was 5436; the average deposit was 5436/144 = 37.75.<br>
The average deposit is the average of the first and last deposits:
(first + last)/2 = 37.75
first + last = 2*37.75 = 75.5  [1]<br>
The last deposit is the first deposit, plus the common difference of 50c = 0.5p 119 times:
last = first + 119(0.5) = first + 59.5  [2]<br>
From [1] and [2]...
first + last = first + first + 59.5 = 75.5
2*first = 16
first = 8  [3]<br>
From [2] and [3], last = 8 + 59.5 = 67.5<br>
ANSWER: He put Php 67.5 in the jar the last month<br>
CHECK: {{{144((8+67.5)/2)=144*37.75=5436}}}<br>