El abuelo, Don José, es de edad avanzada, aunque no es centenario. El año pasado su edad era múltiplo de 8, y el año próximo es múltiplo de 7.

¿Cuantos años tiene Don José?

97

Step-by-step explanation:

This can be translated to:

The Grandfather, Don José, is a old man, but is not over 100 years old.

Last year his age was a multiple of 8, and next year will be a multiple of 7.

Find the age of Don José.

Ok, if the age of Don José is X, we have that:

X is a number of two digits.

X + 1 is a multiple of 7

X - 1 is a multiple of 8.

ok, the multiples of 7 are:

7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91, 98

the multiples of 8 are:

8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96

Now we must find any two numbers (one for each set) that are distanced by 2 units (because the difference between X + 1 and X - 1 is: (X + 1) - (X - 1) = 2)

We also must have that the larger number comes from the set of the multiples of 7, and the smaller number comes from the set of multiples of 8, the numbers are:

98, is multiple of 7 and this is X + 1

96 is multiple of 8 and this is X - 1

then X = 97,

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step-by-step explanation:

just get this app called photo math it should be able to do those