Question 1201373
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You CAN solve the problem using fractions or decimals, as shown in responses from other tutors.  But the actual work to solve the problem is usually easier if we can set the problem up using whole numbers.<br>
Since last month Mr Gan's salary was 9/10 of Mr Koon's salary...<br>
let 9x = Mr. Gan's salary last month
let 10x = Mr. Koon's salary last month<br>
When Mr. Gan's salary decreased by $220 and Mr. Koon's salary increased by $200, Mr. Gan's new salary was 7/10 of Mr Koon's new salary:<br>
{{{(9x-220)/(10x+200)=7/10}}}
{{{7(10x+200)=10(9x-220)}}}
{{{70x+1400=90x-2200}}}
{{{3600=20x}}}
{{{x=180}}}<br>
ANSWER: Mr. Gan's salary last month was 9x = 9($180) = $1620<br>