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Lorna collected 1/3 the number of coins that Mandy collected. Mandy collected two and one quarter (2 1/4) the number of coins collected by Enver. If all three collected 480 coins then how many coins did Mandy collect?

Mathematics

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3 parts
18

270 coins\text{270 coins}

19

40\text{40}

20

96 blue stones\text{96 blue stones}

Step-by-step solution

13 steps

Here are the solutions to the problems:

Part 18· 5 steps

Lorna collected 13\frac{1}{3} the number of coins that Mandy collected. Mandy collected 2142\frac{1}{4} the number of coins collected by Enver. All three collected 480 coins.

  1. Define variables and set up equations.

    Let MM be the number of coins Mandy collected.
    Let LL be the number of coins Lorna collected.
    Let EE be the number of coins Enver collected.
    From the problem:

    1. L=13ML = \frac{1}{3} M
    2. M=214E=94EM = 2\frac{1}{4} E = \frac{9}{4} E
    3. L+M+E=480L + M + E = 480
  2. Express LL and EE in terms of MM.

    From (1), L=13ML = \frac{1}{3} M.
    From (2), we can express EE in terms of MM: E=M÷94=M×49=49ME = M \div \frac{9}{4} = M \times \frac{4}{9} = \frac{4}{9} M.

  3. Substitute LL and EE into the total sum equation.

    13M+M+49M=480\frac{1}{3} M + M + \frac{4}{9} M = 480
  4. Combine the terms with MM.

    Find a common denominator, which is 9.

    39M+99M+49M=480\frac{3}{9} M + \frac{9}{9} M + \frac{4}{9} M = 480 (3+9+49)M=480\left(\frac{3+9+4}{9}\right) M = 480 169M=480\frac{16}{9} M = 480
  5. Solve for MM.

    M=480×916M = 480 \times \frac{9}{16} M=(480÷16)×9M = (480 \div 16) \times 9 M=30×9M = 30 \times 9 M=270M = 270

    Mandy collected 270 coins.

    The final answer is 270 coins\boxed{\text{270 coins}}.

Part 19

40\text{40}

Jakes numbered the houses on a straight road from 80 to 180 using different digits. How many 4's and 8's did Jakes use?

  1. Count the occurrences of the digit '4' in the numbers from 80 to 180.

    • Numbers with '4' in the units place: 84, 94, 104, 114, 124, 134, 144, 154, 164, 174. (10 occurrences)
    • Numbers with '4' in the tens place: 140, 141, 142, 143, 144, 145, 146, 147, 148, 149. (10 occurrences) The number 144 contains two '4's (one in the units place and one in the tens place). Total '4's = 10 (from units place) + 10 (from tens place) = 20.
  2. Count the occurrences of the digit '8' in the numbers from 80 to 180.

    • Numbers with '8' in the units place: 88, 98, 108, 118, 128, 138, 148, 158, 168, 178. (10 occurrences)
    • Numbers with '8' in the tens place: 80, 81, 82, 83, 84, 85, 86, 87, 88, 89. (10 occurrences) The number 88 contains two '8's (one in the units place and one in the tens place). Total '8's = 10 (from units place) + 10 (from tens place) = 20. Wait, I need to be careful with the range. For 8's in the tens place, the numbers are 80-89. For 8's in the units place, the numbers are 88, 98, 108, 118, 128, 138, 148, 158, 168, 178. Let's list them and count: For '8's: 80, 81, 82, 83, 84, 85, 86, 87, 88 (two 8s), 89 (10 numbers, 11 '8's) 98 (1 '8') 108 (1 '8') 118 (1 '8') 128 (1 '8') 138 (1 '8') 148 (1 '8') 158 (1 '8') 168 (1 '8') 178 (1 '8') Total '8's = 11 + 9 = 20.

    Let's re-verify the 8's count.
    Numbers from 80 to 180.
    Units digit is 8: 88, 98, 108, 118, 128, 138, 148, 158, 168, 178. (10 numbers, 10 '8's from units place)
    Tens digit is 8: 80, 81, 82, 83, 84, 85, 86, 87, 88, 89. (10 numbers, 10 '8's from tens place)
    The number 88 has two '8's. So, the total count of '8's is 10 + 10 = 20.

    My previous manual count was 21. Let's re-do it carefully.
    80 (1)
    81 (1)
    82 (1)
    83 (1)
    84 (1)
    85 (1)
    86 (1)
    87 (1)
    88 (2)
    89 (1)
    Subtotal for 80-89: 1+1+1+1+1+1+1+1+2+1 = 11 '8's.

    90-99: 98 (1 '8')
    100-109: 108 (1 '8')
    110-119: 118 (1 '8')
    120-129: 128 (1 '8')
    130-139: 138 (1 '8')
    140-149: 148 (1 '8')
    150-159: 158 (1 '8')
    160-169: 168 (1 '8')
    170-179: 178 (1 '8')
    180: No '8'
    Subtotal for 90-180: 1+1+1+1+1+1+1+1+1 = 9 '8's.

    Total '8's = 11 + 9 = 20.
    So, there are 20 '4's and 20 '8's.

  3. Calculate the total number of 4's and 8's.

    Total = (Number of '4's) + (Number of '8's)
    Total = 20 + 20 = 40.

    The final answer is 40\boxed{\text{40}}.

Part 20

96 blue stones\text{96 blue stones}

The pendant has 108 stones arranged in a pattern: W W B B W W B B B B W W B B B B B B B B ......
The last stone is blue.

  1. Identify the pattern of the stone arrangement.

    The pattern consists of blocks, each starting with two white stones (WW) followed by a number of blue stones (B).
    Block 1: W W B B (2 White, 2 Blue) - Total 4 stones
    Block 2: W W B B B B (2 White, 4 Blue) - Total 6 stones
    Block 3: W W B B B B B B B B (2 White, 8 Blue) - Total 10 stones
    It appears the number of blue stones in each block is a power of 2: 21,22,23,…,2n2^1, 2^2, 2^3, \dots, 2^n.
    So, Block nn has 2 White stones and 2n2^n Blue stones, for a total of 2+2n2 + 2^n stones.

  2. Calculate the cumulative number of stones and blue stones for each full block.

    • Block 1 (n=1n=1): 2W, 212^1B = 2B. Total stones = 4. Cumulative stones = 4. Cumulative blue = 2.
    • Block 2 (n=2n=2): 2W, 222^2B = 4B. Total stones = 6. Cumulative stones = 4 + 6 = 10. Cumulative blue = 2 + 4 = 6.
    • Block 3 (n=3n=3): 2W, 232^3B = 8B. Total stones = 10. Cumulative stones = 10 + 10 = 20. Cumulative blue = 6 + 8 = 14.
    • Block 4 (n=4n=4): 2W, 242^4B = 16B. Total stones = 18. Cumulative stones = 20 + 18 = 38. Cumulative blue = 14 + 16 = 30.
    • Block 5 (n=5n=5): 2W, 252^5B = 32B. Total stones = 34. Cumulative stones = 38 + 34 = 72. Cumulative blue = 30 + 32 = 62.
  3. Determine the remaining stones for the pendant.

    The pendant has a total of 108 stones. After 5 full blocks, 72 stones have been used.
    Remaining stones = 108−72=36108 - 72 = 36 stones.

  4. Analyze the partial block.

    The next block (Block 6, n=6n=6) would start with 2 White stones, followed by 26=642^6 = 64 Blue stones.
    The 36 remaining stones must come from Block 6.
    The first 2 stones of Block 6 are White (WW). So, 2 White stones are added.
    The number of stones remaining to be placed after the 2 white stones is 36−2=3436 - 2 = 34.
    These 34 stones must be blue stones from Block 6. This also satisfies the condition that the last stone is blue.

  5. Calculate the total number of blue stones.

    Total blue stones = (Cumulative blue stones from 5 full blocks) + (Blue stones from the partial 6th block)
    Total blue stones = 62+34=9662 + 34 = 96.

    The final answer is 96 blue stones\boxed{\text{96 blue stones}}.

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