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Data transfer time and bandwidth: Class 12 practice

Transfer time = data size ÷ data rate. Read the method, follow the three worked examples, then try the six questions.

What you should know first

  • Data storage units

The idea behind data transfer time and bandwidth

Transfer time = data size ÷ data rate. Convert carefully: 1 byte = 8 bits, 1 KB = 1024 bytes, and network speeds use 1 Mbps = 10⁶ bits per second.

Step-by-step method

  1. Convert the file size to bits.
  2. Convert the speed to bits per second.
  3. Time = bits ÷ bps.

Worked example 1 (Basic)

How many bits are in 37 KB?

  1. 37 × 1024 × 8
  2. Answer: 303104 bits

Worked example 2 (Standard)

How long does a 39 MB file take to download at 20 Mbps (1 MB = 1024 × 1024 bytes)?

  1. Bits = 39 × 1024² × 8 = 327155712
  2. Time = 327155712 ÷ 20000000 = 16.36 s
  3. Answer: 16.36 s

Worked example 3 (Challenge)

How long does a 430 MB file take to download at 100 Mbps (1 MB = 1024 × 1024 bytes)?

  1. Bits = 430 × 1024² × 8 = 3607101440
  2. Time = 3607101440 ÷ 100000000 = 36.07 s
  3. Answer: 36.07 s

Common mistakes and misconceptions

  • Forgetting the factor 8
  • Mixing 1000 and 1024

Practice questions

  1. (Basic) How many bits are in 40 KB?
  2. (Basic) How many bits are in 2 KB?
  3. (Standard) How long does a 17 MB file take to download at 100 Mbps (1 MB = 1024 × 1024 bytes)?
  4. (Standard) How long does a 8 MB file take to download at 2 Mbps (1 MB = 1024 × 1024 bytes)?
  5. (Challenge) How long does a 30 MB file take to download at 4 Mbps (1 MB = 1024 × 1024 bytes)?
  6. (Challenge) How long does a 210 MB file take to download at 2 Mbps (1 MB = 1024 × 1024 bytes)?

Answer key with full working

  • Q1: 40 × 1024 × 8 → Answer: 327680 bits
  • Q2: 2 × 1024 × 8 → Answer: 16384 bits
  • Q3: Bits = 17 × 1024² × 8 = 142606336 → Time = 142606336 ÷ 100000000 = 1.43 s → Answer: 1.43 s
  • Q4: Bits = 8 × 1024² × 8 = 67108864 → Time = 67108864 ÷ 2000000 = 33.55 s → Answer: 33.55 s
  • Q5: Bits = 30 × 1024² × 8 = 251658240 → Time = 251658240 ÷ 4000000 = 62.91 s → Answer: 62.91 s
  • Q6: Bits = 210 × 1024² × 8 = 1761607680 → Time = 1761607680 ÷ 2000000 = 880.8 s → Answer: 880.8 s

Syllabus note

This skill is listed under "Computer Networks" for Class 12 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.

Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.

Related practice and notes

Frequently asked questions

Which chapter is data transfer time and bandwidth in?

"Computer Networks", Class 12 Computer Science (NCERT/CBSE). Other boards may place it differently.

How were the answers checked?

Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.

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