In a flower decoration the first layer has (42) flowers and each next layer has (11) more flowers. Which layer will have (207) flowers?
Answer and explanation
Correct answer: 16
The numbers of flowers form an AP with first term \(a=42\) and common difference \(d=11\). The number of flowers in the \(n\)th layer is \(a_n=42+(n-1)\times 11\). Putting \(a_n=207\), \(42+(n-1)\times 11=207\), so \((n-1)\times 11=165\), giving \(n-1=15\) and \(n=16\). Hence, the 16th layer has 207 flowers. The 15th layer would have only \(196\) flowers. Exam tip: when a position or layer is asked, equate the target value to \(a_n\) and solve for \(n\).
Frequently asked questions
What is the correct answer to this question?
16
Why is this the correct answer?
The numbers of flowers form an AP with first term \(a=42\) and common difference \(d=11\). The number of flowers in the \(n\)th layer is \(a_n=42+(n-1)\times 11\). Putting \(a_n=207\), \(42+(n-1)\times 11=207\), so \((n-1)\times 11=165\), giving \(n-1=15\) and \(n=16\). Hence, the 16th layer has 207 flowers. The 15th layer would have only \(196\) flowers. Exam tip: when a position or layer is asked, equate the target value to \(a_n\) and solve for \(n\).
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Arithmetic Progressions (AP). Topic: Word problems based on APs.
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