RRB Group D 17-Sep-2018 Shift 2 Solved Paper

Question : 42 of 100

Marks: +1, -0

When

7^{21}+7^{22}+7^{23}+7^{24}

is divided by 25 the remainder is :

Solution:

7^{21}+7^{22}+7^{23}+7^{24}

=7^{21}(1+7+7^{2}+7^{3})

=7^{21}(1+7+49+343)

=\;{7^{21} × 400}\/{25}=7^{21} × 16

exactly divisible & Reminder is Zero.

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