Multiply 8-Digit Numbers

What is 47382916 x 65109472? Don't use tools, do the calculation in your head. Show your working.

159.6s $0.13 Tokens i/o: 711/8,754 Nov 21st

Below, I'll show my step-by-step working for computing 47382916 × 65109472 "in my head" (simulating manual calculation as an AI without external tools). Since these are large numbers, direct digit-by-digit multiplication would be extremely tedious, so I'll use a divide-and-conquer approach by splitting each number into two 4-digit parts. This is a standard way to simplify large multiplications mentally or on paper.

  • 47382916 = 4738 × 10,000 + 2916 (let a = 4738, b = 2916)
  • 65109472 = 6510 × 10,000 + 9472 (let c = 6510, d = 9472)

The product is then (a × 10,000 + b) × (c × 10,000 + d) =
(a × c × 10,000²) + ((a × d) + (b × c)) × 10,000 + (b × d)
= (a × c) × 100,000,000 + ((a × d) + (b × c)) × 10,000 + (b × d)

I'll compute each pairwise multiplication by breaking them down further into smaller multiplications (e.g., using distributive property).

  • a × c = 4738 × 6510
    4738 × 6000 = 28,428,000
    4738 × 500 = 2,369,000
    4738 × 10 = 47,380
    Sum: 28,428,000 + 2,369,000 = 30,797,000; 30,797,000 + 47,380 = 30,844,380

  • a × d = 4738 × 9472
    4738 × 9000 = 42,642,000
    4738 × 400 = 1,895,200
    4738 × 70 = 331,660
    4738 × 2 = 9,476
    Sum: 42,642,000 + 1,895,200 = 44,537,200; 44,537,200 + 331,660 = 44,868,860; 44,868,860 + 9,476 = 44,878,336

  • b × c = 2916 × 6510
    2916 × 6000 = 17,496,000
    2916 × 500 = 1,458,000
    2916 × 10 = 29,160
    Sum: 17,496,000 + 1,458,000 = 18,954,000; 18,954,000 + 29,160 = 18,983,160

  • b × d = 2916 × 9472
    2916 × 9000 = 26,244,000
    2916 × 400 = 1,166,400
    2916 × 70 = 204,120
    2916 × 2 = 5,832
    Sum: 26,244,000 + 1,166,400 = 27,410,400; 27,410,400 + 204,120 = 27,614,520; 27,614,520 + 5,832 = 27,620,352

(a × d) + (b × c) = 44,878,336 + 18,983,160 = 63,861,496

  • (a × c) × 100,000,000 = 30,844,380 × 100,000,000 = 3,084,438,000,000,000
  • Cross term × 10,000 = 63,861,496 × 10,000 = 638,614,960,000
  • b × d remains 27,620,352

Now add them together (starting with the smaller two, then adding to the large one, handling carries as needed):

  • First, 638,614,960,000 + 27,620,352 = 638,642,580,352
  • Now, 3,084,438,000,000,000 + 638,642,580,352
    To add, align and add column-by-column from the right (padding with leading zeros for alignment to 16 digits):
      3084438000000000
    + 0000638642580352
    ------------------
      3085076642580352
    
    (Details of column additions with carries: No carry beyond the existing digits. Key carries occurred in the middle positions, e.g., 8 + 8 = 16 → write 6, carry 1; 3 + 3 + 1 = 7 → no carry; 4 + 6 = 10 → write 0, carry 1; 4 + 0 + 1 = 5 → no carry.)

47382916 × 65109472 = 3,085,076,642,580,352

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