## Que: Mandy sold 600 apples in 10 days. If the number of apples she sold increased by 4 each day.....

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### Que: Mandy sold 600 apples in 10 days. If the number of apples she sold increased by 4 each day.....

by [email protected] Revolution » Tue May 04, 2021 9:35 pm

00:00

A

B

C

D

E

## Global Stats

Que: Mandy sold 600 apples in 10 days. If the number of apples she sold increased by 4 each day, how many apples did she sell on the $$10^{th}$$ day?

A. 36
B. 42
C. 60
D. 78
E. 100

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### Re: Que: Mandy sold 600 apples in 10 days. If the number of apples she sold increased by 4 each day.....

by [email protected] Revolution » Wed May 05, 2021 9:25 pm
Solution: We have to find the number of apples did Mandy sell on the $$10^{th}$$ day.

Given: Mandy sold 600 apples in 10 days and the number of apples she sold increased by 4 each day

$$1^{st}$$ day: x

$$2^{nd}$$ day: x + 4

$$3^{rd}$$ day: x + 4 + 4 = x + 2 * 4 .
.
.
$$10^{th}$$ day: x + 9 * 4

=> x + (x + 4) + (x + 2 * 4) + ….+(x + 9 * 4) = 600

=> 10 x + 4 + 2 * 4 + …..+ 9 * 4 = 600

=> 10x + 4( 1 + 2 + …. + 9) = 600

=> 1 + 2 + 3 + 4 +…..+ n = $$\frac{n\left(n+1\right)}{2}$$

=> 10x + 4[$$\frac{9\cdot10}{2}$$] = 600

=> 10x + 180 = 600

=> 10x = 420

=> x = 42

=> ∴ $$10^{th}$$ day = x + 9*4 = 42 + 36 = 78

Therefore, D is the correct answer.