One square needs 4 matchsticks. Two squares in a row sharing a side need 7 matchsticks, and three squares in a row need 10. How many matchsticks are needed for a row of 20 squares?
Answer and explanation
Correct answer: C. 61
- Step 1: Each extra square adds 3 matchsticks: 4, 7, 10. Step 2. The rule is 3n + 1. Step 3. For 20 squares: 3 × 20 + 1 = 61. Answer: 61. Why not the others: 80: This multiplies 20 by 4, as if the squares did not share sides. 60: This uses 3n and leaves out the + 1. 63: This uses 3n + 3 instead of 3n + 1.
Practise more Multi-step number problems.
Free questions with an explanation for every one, and full timed Independent School Entrance (ISEB Pre-Test and 11+ CEM style) mock tests.
More Multi-step number problems questions
- A cinema sells adult tickets at £9.50 and child tickets at £6.25. A family ticket for 2 adults and 2 children costs £28. What is the cheapes…
- Sound travels at about 340 m/s. A clap of thunder is heard 6 seconds after the lightning flash. How far away is the lightning, in kilometres…
- A school trip has 168 pupils and 12 staff. Each coach seats 52 people. What is the smallest number of coaches needed?
- Eve spends 2/5 of her money on a book, and then 1/3 of what is left on lunch. She has £12 left. How much money did she start with?
- A tap fills a bucket at 15 litres per minute. Each bucket holds 9 litres. How many seconds does it take to fill 5 buckets?
- A paint is mixed from blue and yellow in the ratio 2 : 3. A decorator uses 4.5 litres of blue. How much yellow does she use?