Question 766648
One time period is a day and a night
The frog either advance by +3m or
falls back {{{ 3 - 4 = -1 }}}m
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Let {{{ a }}} = number of periods of +3m gain
Let {{{ b }}} = number of periods of -1m loss
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(1) {{{ a + b = 15 }}} ( the 16th day hasn't happened yet )
(2) {{{ 3a - b = 29 }}}
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Add the equations
{{{ 4a = 44 }}}
{{{ a = 11 }}}
and
(1) {{{ 11 + b = 15 }}} 
(1) {{{ b = 4 }}}
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The frog slept 4 nights
check:
(2) {{{ 3a - b = 29 }}}
(2) {{{ 3*11 - 4 = 29 }}}
(2) {{{ 33 - 4 = 29 }}}
(2) {{{ 29 = 29 }}}
OK