Combined Bank Officer (IT) Exam 3 January 2026 — Question Solution | সমন্বিত ব্যাংক (ব্যাংকার্স সিলেকশন কমিটি) অফিসার (আইটি) নিয়োগ পরীক্ষা ২০২৬ — প্রশ্ন সমাধান

Correct answer: (b) The DNS server is unreachable or misconfigured

Work it out step by step:

1. ping sends ICMP echo requests and checks IP-level connectivity, so a reply from 8.8.8.8 proves the cable, the IP settings, the gateway and the ISP path all work.
2. Opening www.google.com first needs DNS to translate the name into an IP address.
3. Only the name step fails, so the DNS server is unreachable or misconfigured.
   Other options: (a) The ISP gateway is down — then the ping to 8.8.8.8 would fail too; (c) The network cable is unplugged — there would be no connectivity at all, so the ping would fail; (d) The DHCP server is full — DHCP hands out addresses, but this host already has a working one, as the ping proves.

Also know:

• 8.8.8.8 and 8.8.4.4 are the IPv4 addresses of Google Public DNS.
• nslookup shows information for diagnosing DNS infrastructure.
• ipconfig /flushdns clears the DNS client resolver cache during DNS troubleshooting.

Sources: ping – Microsoft Learn; DNS – MDN Web Docs Glossary; Get Started with Google Public DNS – Google for Developers; RFC 2131: Dynamic Host Configuration Protocol – IETF; nslookup – Microsoft Learn; ipconfig – Microsoft Learn

Correct answer: (b) To host public-facing services (Web, Email) separate from the internal LAN

A DMZ is a perimeter network segment logically between the internal and external networks. It gives external, untrusted users restricted access to releasable information while shielding the internal networks from outside attacks (CNSSI 4009, via the NIST glossary). The NIST glossary adds that externally accessible systems needing some protection usually sit on DMZ networks; public web and mail servers, the examples in the option, are such systems, so outsiders never need direct access to the internal LAN.
Other options: (a) the core database holds sensitive data and belongs on the protected internal network, not the zone exposed to outsiders; (c) the CEO's computer is an internal workstation, not a public-facing service; (d) testing viruses needs an isolated lab, not a segment that faces the Internet.

Also know:

• Another name for a DMZ is a perimeter network.
• Traffic between the DMZ and other protected interfaces still passes through the firewall, so firewall policies can be applied to it.
• The DMZ enforces the internal network's security policy for information exchanged with the outside.

Sources: demilitarized zone (DMZ) – NIST CSRC Glossary

Correct answer: (a) Stack

Brackets close in the reverse order of opening (last opened, first closed), which is exactly LIFO. Method: scan left to right; push each opening bracket; on a closing bracket pop the top and check it matches; at the end the stack must be empty.

1. "{[()]}": push {, [, ( → ")" pops ( ✓ → "]" pops [ ✓ → "}" pops { ✓ → empty, so balanced.
2. "(]": push ( → "]" pops ( ✗, so unbalanced.
   Other options: (b) a queue is FIFO and would release the earliest opening bracket first, but the innermost one must close first; (c) a tree can represent a parsed expression but is not used for the matching check; (d) an array can store the characters, yet the matching still needs stack (LIFO) behaviour.

Also know:

• A stack's basic operations are push and pop; top and isEmpty are often provided too.
• A queue is FIFO: only the earliest added item may be accessed.
• Dijkstra's two-stack algorithm evaluates fully parenthesized arithmetic expressions.

Sources: stack – NIST Dictionary of Algorithms and Data Structures; queue – NIST Dictionary of Algorithms and Data Structures; Algorithms 4e, 1.3 Bags, Queues, and Stacks – Princeton University

Correct answer: (c) Controller

In MVC, user requests are routed to a controller. Microsoft's ASP.NET Core documentation says the controller handles and responds to user input, works with the model and then selects a view to render; its action methods are what handle each request (GET, POST and so on).
Other options: (a) Model — holds the application's state and business logic, not the incoming request; (b) View — only presents content through the user interface; (d) Both Model and View — neither one receives HTTP requests; that is the controller's job.

Also know:

• MVC separates data (Model), display (View) and control logic (Controller), a separation of concerns.
• Requests are mapped to controller actions through routing.
• MVVM and MVP are other patterns based on MVC.

Sources: Overview of ASP.NET Core MVC – Microsoft Learn; Handle requests with controllers in ASP.NET Core MVC – Microsoft Learn; MVC – MDN Web Docs Glossary

Correct answer: (c) SJF

Shortest Job First runs the shortest job next, so short jobs never wait behind long ones. OSTEP notes SJF is optimal when all jobs arrive together (it measures turnaround time; with all arrivals at time 0, waiting time = turnaround time − burst time, and the bursts are fixed, so the same order also minimises average waiting time). Example with bursts A = 100, B = 10, C = 10:

1. FCFS (A, B, C): waits 0, 100, 110; average = 210 ÷ 3 = 70.
2. SJF (B, C, A): waits 0, 10, 20; average = 30 ÷ 3 = 10.
   Other options: (a) FCFS — suffers the convoy effect: short jobs queue behind a long one; (b) Round Robin — good for response time but one of the worst policies for turnaround time (OSTEP), so it does not minimise waiting; (d) Priority — orders jobs by priority, not length, so a long high-priority job can delay short ones.

Also know:

• For the same jobs, average turnaround time is (100+110+120) ÷ 3 = 110 under FCFS and (10+20+120) ÷ 3 = 50 under SJF.
• The preemptive version of SJF is Shortest Time-to-Completion First (STCF), also called Preemptive SJF (PSJF); it handles jobs that arrive late.
• SJF assumes the scheduler knows the length of each job, which real systems usually do not.

Sources: Scheduling: Introduction – OSTEP (Arpaci-Dusseau, Univ. of Wisconsin)

Correct answer: (c) 38.4 sec

1. To clear the tunnel the train covers its own length plus the tunnel: 220 + 260 = 480 m.
2. Speed: 45 km/h = 45 × 1000 ÷ 3600 = 12.5 m/s.
3. Time = distance ÷ speed (HyperPhysics) = 480 ÷ 12.5 = 38.4 s.
   Check: 12.5 × 38.4 = 480 ✓ (and 45 × 5/18 = 12.5).
   Other options: (a) 25.4 sec — covers only 12.5 × 25.4 = 317.5 m; (b) 35.4 sec — covers 442.5 m, short of 480 m; (d) 40.4 sec — covers 505 m, more than needed.

Also know:

• Average speed is distance travelled divided by time elapsed (HyperPhysics).
• To pass a pole or a person the train covers only its own length: 220 ÷ 12.5 = 17.6 s.
• km/h → m/s: multiply by 5/18; m/s → km/h: multiply by 18/5.

Sources: Velocity – HyperPhysics (Georgia State University)

Correct answer: (b) National Payment Switch Bangladesh

NPSB stands for National Payment Switch Bangladesh. Bangladesh Bank launched it in 2012 to connect financial institutions and make card and account transactions interoperable across banks (ATM, POS, internet-banking transfers).
Other options: (a) National Payment System of Banks — not the expansion; (c) National Processing Service Bureau — not a Bangladeshi payment system; (d) Network Payment and Settlement Board — not a real body or system.

Also know:

• BD-RTGS (Real Time Gross Settlement) handles high-value, time-critical transfers.
• BEFTN is the Bangladesh Electronic Fund Transfer Network; BACH is the Bangladesh Automated Clearing House.
• TakaPay, Bangladesh's national card scheme, aims to reduce dependence on international card networks.

Sources: Bangladesh Payment Systems Report 2025 – Bangladesh Bank; Payment Systems – Bangladesh Bank