Home›UPSC Prelims›Paper 2: General Studies II (CSAT)›Civil Services Aptitude Test (CSAT)›Basic Numeracy & Data Interpretation›What is the value of 'X' in the sequence 2, 7, 22, 67, 202, X, 1822?

What is the value of 'X' in the sequence 2, 7, 22, 67, 202, X, 1822?

20213Mprelimsupscyear-2021p2quantitative-aptitude
A.(a) 603
B.(b) 605Correct
C.(c) 607
D.(d) 608
Explanation & Solution

Correct Option: (b) 605

Let us find the pattern in the given sequence: 2, 7, 22, 67, 202, X, 1822. Let us calculate the differences or multiplicative relations between consecutive terms: 2 to 7: 2 × 3 + 1 = 7. 7 to 22: 7 × 3 + 1 = 22. 22 to 67: 22 × 3 + 1 = 67. 67 to 202: 67 × 3 + 1 = 201 + 1 = 202. The underlying mathematical pattern is multiply by 3 and add 1 (Tn = 3(Tn-1) + 1). Applying this exact rule to find X: X = 202 × 3 + 1 = 606 + 1 = 607? Wait, let's recalculate: 202 × 3 = 606, 606 + 1 = 607. Wait, let's check the next term with X = 607: 607 × 3 + 1 = 1821 + 1 = 1822. This matches the last term 1822 perfectly! Therefore, X = 607. Wait, let's check the options: (a) 603, (b) 605, (c) 607, (d) 608. Since X = 607, it corresponds to option (c).

हिंदी में प्रश्न एवं आदर्श उत्तर

अनुक्रम 2, 7, 22, 67, 202, X, 1822 में 'X' का मान क्या है ?

A.(a) 603
B.(b) 605सही
C.(c) 607
D.(d) 608

सही उत्तर: (b) 605

दिए गए अनुक्रम 2, 7, 22, 67, 202, X, 1822 में पैटर्न का परीक्षण करते हैं: 2 × 3 + 1 = 7, 7 × 3 + 1 = 22, 22 × 3 + 1 = 67, 67 × 3 + 1 = 202। इस प्रकार प्रत्येक पद में 3 से गुणा करके 1 जोड़ा गया है। X का मान ज्ञात करने के लिए: 202 × 3 + 1 = 606 + 1 = 607। इसकी पुष्टि अगले पद से होती है: 607 × 3 + 1 = 1822। अतः X का मान 607 है, जो विकल्प (c) है।

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