Question

# Mohan saves Rs. $$1$$ on the first day, Rs. $$2$$ on the second day, Rs. $$3$$ on the third day and so on. What will be his total saving after $$40$$ days?

Solution

## Mohan's savings are Rs. $$1$$, Rs. $$2$$, Rs. $$3$$,.... Here, $${ t }_{ 1 }=1$$, $$n=40$$Therefore, $${ t }_{ n }={ t }_{ 40 }=20$$; $${ S }_{ n }={ S }_{ 40 }=$$?$$\Rightarrow { S }_{ n }=\dfrac { n }{ 2 } \left( { t }_{ 1 }+{ t }_{ n } \right)$$$$\Rightarrow { S }_{ 40 }=\dfrac { 40 }{ 2 } \left( 1+40 \right)$$$$\Rightarrow { S }_{ 40 }=\dfrac { 40 }{ 2 } \times 41=820$$Hence, Mohan's total savings after $$40$$ days will be Rs. $$820$$.Mathematics

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