Home › CA Foundation › quantitativeaptitude › Number Series, Coding and Decoding and Odd Man Out › Find next: 1, 3, 6, 10, 15, ?
Find next: 1, 3, 6, 10, 15, ?
A21
B22
C20
D18
Answer & Solution
Correct answer: A. 21
1. Triangular numbers: T_n = n(n+1)/2.
2. Check: T_1=1, T_2=3, T_3=6, T_4=10, T_5=15.
3. Next is T_6 = 6*7/2 = 21.
4. So missing term is 21.
_Source: ICAI BoS Foundation Paper 3, Ch 9 'Series', p.4_
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