Ahmad bought a mobile phone with 40% of his money and an electronic dictionary that cost $90 less than the mobile phone. He spent $310, how much money did he have at first?
x = Ahmad"s money
Ahmad bought a mobile phone with 40% of his money means:
Ahmad spend 40 / 100 x = 0.4 x
on mobile phone.
An electronic dictionary that cost $90 less than the mobile phone means electronic dictionary cost:
0.4 x - $90
He totaly spend:
0.4 x + 0.4 x - $90 =
0.8 x - $90
He spent $310 means:
0.8 x - $90 = $310
Add $90 to both sides
0.8 x = $400
x = $400 / 0.8
x = $500
He have $500
Check result:
He spend 0.4 x = 0.4 • 500 = $200
on mobile phone
He spend $200 - $90 = $110
on electronic dictionary.
$200 + $110 = $310