Math Series #4

Number Theory Level 2

Find the value of 38295 × 99999 38295 \times 99999 . (Try to find a way to solve it without using a calculator)


The answer is 3829461705.

Avner Lim by Avner Lim , 38, Indonesia

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2 solutions

Chew-Seong Cheong
Mar 10, 2021

38295 × 99999 = 38295 × ( 100000 − 1 ) = 3829500000 − 38295 = 3829400000 + 99999 + 1 − 38295 = 3829400000 + 61704 + 1 = 3829461705 \begin{aligned} 38295 \times 99999 & = 38295 \times (100000 - 1) \\ & = 3829500000 - 38295 \\ & = 3829400000 + \blue{99999} + 1 - \blue{38295} \\ & = 3829400000 + \blue{61704} + 1 \\ & = \boxed{3829461705} \end{aligned}

2 Helpful 0 Interesting 1 Brilliant 0 Confused

Round 99999 to 100000 So 38295 x 100000 = 3829500000 And we just need to subtract 38295 from it 3829500000-38295=3829461705

1 Helpful 1 Interesting 2 Brilliant 1 Confused

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