Let the number of P100's be x Let the number of P50's be y Value Value Type Number of of of of EACH ALL bill bills bill bills ------------------------------------------- P100s x P100 P100x P50s y P50 P50y ------------------------------------------- TOTALS 117 ----- P9950 The first equation comes from the second column.x + y = 117 The second equation comes from the last column. 100x + 50y = 9950 So we have the system of equations: . We solve by substitution. Solve the first equation for y: x + y = 117 y = 117 - x Substitute (117 - x) for y in 100x + 50y = 9950 100x + 50(117 - x) = 9950 100x + 5850 - 50x = 9950 50x + 5850 = 9950 50x = 4100 x = 82 = the number of P100s. Substitute in y = 117 - x y = 117 - (82) y = 35 P50s. Checking: 82 P100s is P8200 and 35 P50s is P1750 That's 117 bills. And indeed P8200 + P1750 = P9950 Edwin
The problem can also be done using only one unknown or variable: Let the number of P100s be x Then the number of P50s, using ONE PART = TOTAL MINUS OTHER PART, is 117-x. Value Value Type Number of of of of EACH ALL bill bills bill bills ------------------------------------------- P100s x P100 P100x P50s 117-x P50 P50(117-x) ------------------------------------------- TOTALS 117 ----- P9950 The equation comes from the column on the right100x + 50(117-x) = 9950 100x + 50(117-x) = 9950 100x + 5850 - 50x = 9950 50x + 5850 = 9950 50x = 4100 x = 82 = the number of P100s. The number of P50s is 117-x or 117-82 or 35 P50s. Checking: 82 P100s is P8200 and 35 P50s is P1750 That's 117 coins. And indeed P8200 + P1750 = P9950 Edwin