Concept:
Use suit classification:
- Black cards = Spades + Clubs
- Red cards = Hearts + Diamonds
and form equations based on given ratios.
Step 1:Let number of spades = $x$.
Then:
\[
\text{Diamonds} = 2x,\quad \text{Hearts} = 2 \times (2x) = 4x
\]
Step 2:Use total cards.}
\[
x + 2x + 4x + \text{Clubs} = 13
\Rightarrow 7x + \text{Clubs} = 13 \quad \cdots (1)
\]
Step 3:Use black cards condition.}
\[
\text{Spades} + \text{Clubs} = 7
\Rightarrow x + \text{Clubs} = 7 \quad \cdots (2)
\]
Step 4:Solve equations.}
From (2):
\[
\text{Clubs} = 7 - x
\]
Substitute into (1):
\[
7x + (7 - x) = 13
\Rightarrow 6x + 7 = 13
\Rightarrow 6x = 6
\Rightarrow x = 1
\]
Step 5:Find number of clubs.}
\[
\text{Clubs} = 7 - 1 = 6
\]
But rechecking total cards:
\[
1 + 2 + 4 + 6 = 13 \quad \checkmark
\]
Final Answer:
\[
{6}
\]