Maths P5
posted by jo .
Daniel, Susan and Rick bought some cookies to sell. The cookies were sold at 6 for $2. Daniel sold 1/4 of the cookies. Susan sold 2/7 as many cookies as Rick. Daniel and Susan sold a total of 120 cookies.
a)How many cookies did they sell altogether?
b)How much did they collect from the cookies sold?
c)If the cookies costs $0.20 each, how much profit did they make from the sale?

X = total # of cookies bought.
X/4 = The # of cookies sold by Daniel.
Y = The # of cookies sold by Rick.
2Y/7 = The # of cookies sold by Susan.
X/4 + 2Y/7 = 120 = The # of cookies sold by Daniel and Susan.
Multiply both sides by 28:
Eq1: 7x + 8y = 3360.
y = x  120,
Eq2: x  y = 120.
Multiply Eq2 by 8 and add to Eq1:
7x + 8y = 3360
8x  8y = 960
Sum: 15x = 4320,
X = 288 = The # of cookies sold. 
b. Amt = $2/6 * 288 = $96.
c. Cost = $.20 * 288 = $57.60.
Profit = $96  $57.60 = $38.40.