perplexus.info :: Just Math : Evaluate the missing digit

Evaluate the missing digit (Posted on 2018-01-29)

If the tens digit (second from the right)
of the product p = 2z7 * 39 is 9,
find the digit z.

No Solution Yet Submitted by Ady TZIDON

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Solution

Comment 1 of 1

2z7 * 39

= 2z7*9 + 2z7*30

The tens digit of the first product is 9z+6

The tens digit of the second product is 1

So the tens digit of p is the unit digit of 9z+7

9z+7 ends in 9

9z ends in 2

9z = 72

z=8

check:

287*39 = 11193

Posted by Jer on 2018-01-29 09:48:02

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