A sum of rupees 3125 is to be given in the from of 75 prices. If a price is either rupees 25 or rupees 50 find the number of prices of each type.
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Let's call Rs. 10 x and Rs. 20 y:
x+y= 50
If we subtract y from both sides we get:
x= 50-y
It makes sense, right? If I take the Rs. 20 notes out of the total of 50 notes, then I am left with just the Rs. 10 notes. So remember this value of x, we will use it in the next equation:
10x+20y= 800 Now substitute for x:
10(50-y)+20y= 800
500-10y+20y= 800 Subtract -10y+20y on left and subtract 500 on both sides:
10y= 300
y= 30 You have 30 notes of 20 Rs. and:
50-30= 20 notes of 10 Rs.
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Proof:
30(20)= 600
20(10)= 200
_ _ _ _ ----
Total..: 800 We have the correct answer
x+y= 50
If we subtract y from both sides we get:
x= 50-y
It makes sense, right? If I take the Rs. 20 notes out of the total of 50 notes, then I am left with just the Rs. 10 notes. So remember this value of x, we will use it in the next equation:
10x+20y= 800 Now substitute for x:
10(50-y)+20y= 800
500-10y+20y= 800 Subtract -10y+20y on left and subtract 500 on both sides:
10y= 300
y= 30 You have 30 notes of 20 Rs. and:
50-30= 20 notes of 10 Rs.
------------------------
Proof:
30(20)= 600
20(10)= 200
_ _ _ _ ----
Total..: 800 We have the correct answer
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