JEE Main 2014 · 11 Apr · Shift 1 · Mathematics Q69

MathematicsSingle correct+4 / -1Question 69 of 90

The sum of the first 20 terms common between the series $3+7+11+15+\dots$ and $1+6+11+16+\dots$ , is :

4000

4020

4200

4220

Answer and worked solution

Official answer: B

$3+4k$ and $1+5m$ share the terms $11,31,51,\dots$ (difference 20). The sum of the first 20 is
$\frac{20}2(2\cdot11+19\cdot20)=10\times402=4020.$

JEE Main 2014 · 11 Apr · Shift 1, Mathematics question 69