A boy multiplied 423 by a certain number and obtained 65589 as his answer. If both the 5s in the answer are wrong, but the other figures are right, find the correct answer.
Apparent observation of the results tell me that the multiplier should end with a three, and should be between 140 and 160.
The possible multiplicants therefore are 143, 153 and 163.
Trying to multiply (don't need to go all the way ... just check upto 2 digits - 153 and 163 don't give 89 as the last 2 digits). Multiply 423 with 143 to arrive at the answer.
Hope that helps.
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