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# If a, b, c, and d are positive integers, what is the value of (a + b)

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Re: If a, b, c, and d are positive integers, what is the value of (a + b) [#permalink]
Nidzo wrote:
1)

Given that factorials are the product of the number itself and of all positive integers preceding it, the only way that $$4*a!$$ equals the factorial $$b!$$ is if $$b = 3$$ and $$a = 4$$.

Therefore we have $$(3+4)(c+d)$$. However, we have no information on C and D though.

INSUFFICIENT

2)

Here $$d = 5$$, and $$c = 4$$ for the same reason as mentioned in 1).

Here we have $$(a+b)(4+5)$$. No information regarding a and b.

INSUFFICIENT

1+2) Together we get: $$(3+4)(4+5)$$

$$7*9= 63$$

SUFFICIENT

Here a=3 and b=4, not vice versa.
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Re: If a, b, c, and d are positive integers, what is the value of (a + b) [#permalink]
If a, b, c, and d are positive integers, what is the value of (a + b)(c + d)?

(1) 4*a! = b!
(2) 5*c! = d!

Hi Experts,

Can someone pls explain how is it C?
Re: If a, b, c, and d are positive integers, what is the value of (a + b) [#permalink]
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