Sample Question 12:

Rohan keeps a total of \(90\) guppies in \(4\) fish tanks.

• There is \(1\) more guppy in the \(2\)nd tank than the \(1\)st tank.

• There are \(2\) more guppies in the 3rd tank than the \(2\)nd tank.

• There are \(3\) more guppies in the 4th tank than the \(3\)rd tank.

How many guppies are in the \(4\)th tank?

\(\textbf{(A)}\ 20 \qquad \textbf{(B)}\ 21 \qquad \textbf{(C)}\ 23 \qquad \textbf{(D)}\ 24 \qquad \textbf{(E)}\ 26\)

---

Answer Keys

Question 12: E

---

Solutions

Question 12
Step 1: Begin by understanding the problem statement and what it's asking. Define the variable \(x\) to denote the number of guppies in the first tank.

Step 2: From the given information, calculate the number of guppies in the other tanks:
- The 2nd tank has \(x + 1\) guppies.
- The 3rd tank has \(x + 1 + 2\) guppies.
- The 4th tank has \(x + 1 + 2 + 3\) guppies.

Step 3: According to the problem, the total number of guppies in all tanks is \(90\). Develop an equation to represent this.
- \(x + x + 1 + x + 1 + 2 + x + 1 + 2 + 3 = 90\)

Step 4: Simplify the developed equation, which results in \(4x + 10 = 90\).

Step 5: Solve the equation for \(x\), resulting in \(x = 20\).

Step 6: Find the number of guppies in the 4th tank using the calculated value of \(x\). The 4th tank has \(20 + 1 + 2 + 3 = 26\) guppies.

Hence, the solution to the question "How many guppies are in the 4th tank?" is \(26\). This corresponds to Answer Choice \(\textbf{(E)}\ 26\).