Question

What is the sum of the numbers common to the 2 series
3,6,9,12….100 terms
4,8,12…....80 terms

• A. 2400
• B. 4500
• C. 3900
• D. 6400

Answer 1

The correct option is C 3900

Last term of 1^st AP= 3+(99)3= 300

Last term of 2^nd AP= 4+ (79)4= 320

Hence the common terms starts from 12 and end at 300 with a common difference of 12

Number of terms= (300-12)/12 +1= 25

Sum to 25 terms = 25/2 (12+300) = 3900