Question Detail

In the series 3, 9, 15.. what will be the 21st term ?

  • 123
  • 126
  • 129
  • 136

Answer: Option A

Explanation:

We can judge that it is A.P.
With 6 as difference
nth term in A.P. = a+(n-1)d
a= 3, n = 21, d = 6
So, 21st term will be = 3+(20)6 = 123
Similar Questions :

1. Complete the series
1,6,13,22,33,...

  • 46
  • 48
  • 49
  • 51

Answer: Option A

Explanation:

Pattern is +5, +7, +9, +11
So next number will be +13
=> 33+13 = 46

2. 21,25,33,49,81, ?

  • 140
  • 145
  • 147
  • 159

Answer: Option B

Explanation:

Pattern is, +4, +8, +16, +32, so next will be +64
81+64 = 145

3. 11, 12, 17, 18, 23, 24, (....) . Which term will come next ?

  • 27
  • 29
  • 31
  • 33

Answer: Option B

Explanation:

Please check, given sequence is combination of two seies
[Note: Usually when terms are more than 5, then chances are there that it may contain 2 series.]

Series 1 = 11, 17, 23
Series 2 = 12, 18, 24

So there is pattern +6 in each term
Next term will be 23+6 = 29

4. Complete the series 95, 115.5, 138, ..., 189

  • 160.5
  • 162.5
  • 164.5
  • 166.5

Answer: Option B

Explanation:

Pattern in the series is, +20.5 , +22.5,
Next will be +24.5
138 + 24.5 = 162.5

5. Which fraction will come next, \begin{aligned} \frac{1}{2}, \frac{3}{4}, \frac{5}{8}, \frac{7}{16}, ? \end{aligned}

  • \begin{aligned} \frac{11}{32} \end{aligned}
  • \begin{aligned} \frac{9}{28} \end{aligned}
  • \begin{aligned} \frac{9}{30} \end{aligned}
  • \begin{aligned} \frac{9}{32} \end{aligned}

Answer: Option D

Explanation:

Numerators of the fractions in the given sequence are getting increased by 2, i.e. 1+2,3+2,5+2, so next will be 7+2 = 9

Denominators of the fractions in the series is getting doubled, 2*2 = 4, 4*2 = 8, 8*2 = 16, no next will be 16*2 = 32

So resulting fraction will be
\begin{aligned}
\frac{9}{32}
\end{aligned}

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