Q1.
Let us revise multiplication by 10s and 100s. a) 4 × 10 = ___ b) 20 × 10 = ___ c) 10 × 40 = ___ d) 10 × 10 = 100 e) 20 × 50 = ___ f) 80 × 10 = ___ g) 3 × 100 = 100 × 3 = 300 h) 8 × 100 = ___ = ___ i) 10 × 100 = ___ = ___
Answer
Here are all the answers.
| Question | Answer | Think of it as |
|---|---|---|
| a) 4 × 10 | 40 | 4 tens |
| b) 20 × 10 | 200 | 20 tens |
| c) 10 × 40 | 400 | 40 tens |
| d) 10 × 10 | 100 | 10 tens (given) |
| e) 20 × 50 | 1,000 | 2 × 5 × 10 × 10 = 10 × 100 |
| f) 80 × 10 | 800 | 80 tens |
| g) 3 × 100 | 100 × 3 = 300 | 3 hundreds (given) |
| h) 8 × 100 | 100 × 8 = 800 | 8 hundreds |
| i) 10 × 100 | 100 × 10 = 1,000 | 10 hundreds |
To multiply by 10
Step 1. Take the number.
Step 2. Shift every digit one place to the left.
Step 3. Write 0 in the empty ones place.
Example: 4 → 40, 20 → 200, 80 → 800
Step 1. Take the number.
Step 2. Shift every digit one place to the left.
Step 3. Write 0 in the empty ones place.
Example: 4 → 40, 20 → 200, 80 → 800
Why the zero appears: Multiplying by 10 makes a number ten times bigger. A digit that was worth ones is now worth tens, and a digit that was worth tens is now worth hundreds. Every digit moves one house to the left, and the ones house is left empty — so we write 0 there to hold the place.
For 100, shift twice. 8 × 100: the 8 moves from the ones place to the hundreds place, and two zeros fill the gap — 800. For 1,000, shift three times.