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iwillsurvive101
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If a = positive, and unit digit of a^2 = 9 and units digit of (a+1)^2 is 4, what is the unit digit of (a+2)^2?
The explanation in GMATPrep does not make sense to me.
Here is how I approached it, but not going anywhere with this solution.
- For Unit digit problems, my approach is to always find out individual unit digits, add them(or multiple etc).
(a+1)^2 = a^2 + 2a + 1 --> The addition of these 3 terms leave a unit digit of 4.
a^2(leaves unit digit of 9) + 1 + 2a = should leave 4 in unit
10 + 2a = should leave 4 in unit digit.
=> 2a has to have a 4 in the unit place
Possible values of a to test are a=2, a=6
If a =2 ==> (a+2) ^2 = 8 (not one of the given answer choice)
If a =6 ==> (a+a) ^2 = 64 (not one of the given ans choice)
I am stuck!
Btw Possible answer choices (1, 3, 5, 6, 14)
The explanation in GMATPrep does not make sense to me.
Here is how I approached it, but not going anywhere with this solution.
- For Unit digit problems, my approach is to always find out individual unit digits, add them(or multiple etc).
(a+1)^2 = a^2 + 2a + 1 --> The addition of these 3 terms leave a unit digit of 4.
a^2(leaves unit digit of 9) + 1 + 2a = should leave 4 in unit
10 + 2a = should leave 4 in unit digit.
=> 2a has to have a 4 in the unit place
Possible values of a to test are a=2, a=6
If a =2 ==> (a+2) ^2 = 8 (not one of the given answer choice)
If a =6 ==> (a+a) ^2 = 64 (not one of the given ans choice)
I am stuck!
Btw Possible answer choices (1, 3, 5, 6, 14)
