Tom and Jerry each start a new job. Tom is paid $30,000 in the first year, and in every subsequent year, his annual pay will increase by $1,500. Jerry is paid $25,000 in the first year, and in every subsequent year, his annual pay will increase by 5%.
If they both start working at the beginning of 2013,
- (i)
what is the first year in which Jerry will be paid more than Tom?
- (ii)
at the end of which year will Jerry's total income first exceed Tom's total income?
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Worked solution
4(i)
1. Express Tom's annual pay in the $n$th year
Let be Tom's pay in the th year. Since his pay increases by a constant $1,500 each year, it forms an arithmetic progression with first term and common difference .
2. Express Jerry's annual pay in the $n$th year
Let be Jerry's pay in the th year. Since his pay increases by 5% each year, it forms a geometric progression with first term and common ratio .
3. Formulate the inequality to find when Jerry's pay exceeds Tom's
We require :
4. Solve the inequality using a Graphing Calculator (GC)
This mixed exponential-polynomial inequality cannot be solved algebraically. Using a graphing calculator to generate a table of values for and :
When , and , so .
When , and , so .
The smallest integer is .
5. Determine the actual calendar year
The 1st year () is 2013.
The 17th year is .
Therefore, the first year Jerry will be paid more than Tom is 2029.
2029
4(ii)
1. Formulate an expression for Tom's total income after $n$ years.
Tom's annual pay forms an arithmetic progression with first term and common difference .
Let be his total income after years.
2. Formulate an expression for Jerry's total income after $n$ years.
Jerry's annual pay forms a geometric progression with first term and common ratio .
Let be his total income after years.
3. Set up the inequality and find the smallest integer $n$ using a graphing calculator.
We require Jerry's total income to exceed Tom's total income:
Using the table function on a graphing calculator:
When , and (so )
When , and (so )
The inequality is first satisfied when .
4. Determine the corresponding calendar year.
The 1st year corresponds to 2013.
The 26th year corresponds to .
Jerry's total income will first exceed Tom's at the end of 2038.
2038
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