Random Stuffs: maths question challenge

Tuesday, August 3, 2010

mysterious person X has 420 coins, the total value of them equaling $156.

s/he only has 20 and 50 cent coins though!

how many of each coin does s/he have?

this question was in my sisters textbook and it kinda fucked with me a bit. help me out?

Brian said...: let x = number of 20c
let y = number of 50c

must equal 15600 cents (156 x 100)

set up simultaneous equations
x + y = 420 ------> x = 420 - y
20x + 50y = 15600

Therefore 20(420 - y) + 50y = 15600
8400 - 20y + 50y = 15600
30y = 7200
y = 240

Therefore there are 240 50c pieces

Sub into x + y = 420
x + 240 = 420
x = 180

Therefore there are 180 20c pieces

CHECK

180(0.2) + 240(0.5) = $156

Therefore true

QED

Hope i got it right; Wednesday, August 4, 2010 at 4:20:00 PM GMT+10
Șмž said...: thank you brian!
the answer was indeed 240 50c and 180 20c coins.

how easy it was after all...

but my sisters textbook doesn't do it with simultanious equations, because they haven't learnt that yet. so that's kinda crazy.; Wednesday, August 4, 2010 at 7:50:00 PM GMT+10
Brian said...: you're welcome; Wednesday, August 4, 2010 at 8:36:00 PM GMT+10
Lord of the Palmtrees said...: *IMPLODEs*
you cool kidz!
oh and if simultaneous equations dont do it, her textbook probs want some guess and checking to be done. and damn long and worthless process; Wednesday, August 4, 2010 at 9:40:00 PM GMT+10