Study guides › Level 6 · Master

Friendly numbers: × 25, × 50 and × 125

Level 6 · Master · for questions like “25 × 36 = ?”

💡 The idea

Some numbers pair up into round ones: 25 × 4 = 100, 50 × 2 = 100 and 125 × 8 = 1,000. Look for that pair hiding inside the other number.

🪜 The steps

1. Split the other number into groups of 4 (for 25), 2 (for 50) or 8 (for 125).
2. Each group makes 100 (or 1,000).
3. Count the groups.

✏️ Worked examples

1. 25 × 36: 36 = 9 groups of 4, and each group × 25 = 100. So 900.

2. 125 × 24: 24 = 3 groups of 8, and each × 125 = 1,000. So 3,000.

⚠️ Watch out

• Check the split is exact. 36 ÷ 4 = 9, with nothing left over.
• Another way for × 25: × 100, then ÷ 4.

🎯 Try these

1. 25 × 28
2. 50 × 46
3. 125 × 16

Answers: 1) 700 2) 2,300 3) 2,000

This guide is also in the 10MathQ app: tap “📖 Study guide” after a question.