A plant is (25) cm tall on the first day and grows (1.5) cm daily. What will be its height on the (30)th day?
Answer and explanation
Correct answer: 68.5 cm
This is an arithmetic progression with first term \(a=25\) cm and common difference \(d=1.5\) cm. The \(n\)th term is \(a_n=a+(n-1)d\). Therefore, \(a_{30}=25+(30-1)\times1.5=25+43.5=68.5\) cm. Hence, 68.5 cm is correct. The value 70 cm can result from incorrectly adding \(30\times1.5\); the plant grows only 29 times after the first day. Exam tip: use \((n-1)d\), not \(nd\), for the \(n\)th term of an AP.
Frequently asked questions
What is the correct answer to this question?
68.5 cm
Why is this the correct answer?
This is an arithmetic progression with first term \(a=25\) cm and common difference \(d=1.5\) cm. The \(n\)th term is \(a_n=a+(n-1)d\). Therefore, \(a_{30}=25+(30-1)\times1.5=25+43.5=68.5\) cm. Hence, 68.5 cm is correct. The value 70 cm can result from incorrectly adding \(30\times1.5\); the plant grows only 29 times after the first day. Exam tip: use \((n-1)d\), not \(nd\), for the \(n\)th term of an AP.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Arithmetic Progressions (AP). Topic: Finding the $n$th term of an AP.
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